diff --git a/examples/amm/src/contract.rs b/examples/amm/src/contract.rs
index cef6457044c3..47e27ee5e198 100644
--- a/examples/amm/src/contract.rs
+++ b/examples/amm/src/contract.rs
@@ -326,6 +326,9 @@ impl AmmContract {
                     "Unauthorized"
                 )
             }
+            AccountOwner::Chain => {
+                panic!("Using chain balance is not authorized")
+            }
         }
     }
 
diff --git a/examples/fungible/src/contract.rs b/examples/fungible/src/contract.rs
index db3c9c1ea347..8362b1496458 100644
--- a/examples/fungible/src/contract.rs
+++ b/examples/fungible/src/contract.rs
@@ -143,6 +143,9 @@ impl FungibleTokenContract {
                     "The requested transfer is not correctly authenticated."
                 )
             }
+            AccountOwner::Chain => {
+                panic!("Chain account is not supported")
+            }
         }
     }
 
diff --git a/examples/gen-nft/src/contract.rs b/examples/gen-nft/src/contract.rs
index 8d5f9b420acd..3b989d798f08 100644
--- a/examples/gen-nft/src/contract.rs
+++ b/examples/gen-nft/src/contract.rs
@@ -140,6 +140,9 @@ impl GenNftContract {
                     "The requested transfer is not correctly authenticated."
                 )
             }
+            AccountOwner::Chain => {
+                panic!("Chain account is not supported")
+            }
         }
     }
 
diff --git a/examples/matching-engine/src/contract.rs b/examples/matching-engine/src/contract.rs
index 5462238ae279..c879214a8312 100644
--- a/examples/matching-engine/src/contract.rs
+++ b/examples/matching-engine/src/contract.rs
@@ -166,6 +166,9 @@ impl MatchingEngineContract {
                     "Unauthorized"
                 )
             }
+            AccountOwner::Chain => {
+                panic!("Chain account is not supported")
+            }
         }
     }
 
diff --git a/examples/native-fungible/src/contract.rs b/examples/native-fungible/src/contract.rs
index f80b1882cbe5..e5df39565d9b 100644
--- a/examples/native-fungible/src/contract.rs
+++ b/examples/native-fungible/src/contract.rs
@@ -38,9 +38,9 @@ impl Contract for NativeFungibleTokenContract {
         for (owner, amount) in state.accounts {
             let account = Account {
                 chain_id: self.runtime.chain_id(),
-                owner: Some(owner),
+                owner,
             };
-            self.runtime.transfer(None, account, amount);
+            self.runtime.transfer(AccountOwner::Chain, account, amount);
         }
     }
 
@@ -63,7 +63,7 @@ impl Contract for NativeFungibleTokenContract {
                 let fungible_target_account = target_account;
                 let target_account = self.normalize_account(target_account);
 
-                self.runtime.transfer(Some(owner), target_account, amount);
+                self.runtime.transfer(owner, target_account, amount);
 
                 self.transfer(fungible_target_account.chain_id);
                 FungibleResponse::Ok
@@ -129,7 +129,7 @@ impl NativeFungibleTokenContract {
     fn normalize_account(&self, account: fungible::Account) -> Account {
         Account {
             chain_id: account.chain_id,
-            owner: Some(account.owner),
+            owner: account.owner,
         }
     }
 
@@ -144,6 +144,9 @@ impl NativeFungibleTokenContract {
                 );
             }
             AccountOwner::Application(_) => panic!("Applications not supported yet"),
+            AccountOwner::Chain => {
+                panic!("Chain accounts are not supported")
+            }
         }
     }
 }
diff --git a/examples/non-fungible/src/contract.rs b/examples/non-fungible/src/contract.rs
index 765ca97e866f..569c1352e310 100644
--- a/examples/non-fungible/src/contract.rs
+++ b/examples/non-fungible/src/contract.rs
@@ -144,6 +144,9 @@ impl NonFungibleTokenContract {
                     "The requested transfer is not correctly authenticated."
                 )
             }
+            AccountOwner::Chain => {
+                panic!("Chain account is not supported")
+            }
         }
     }
 
diff --git a/linera-base/src/identifiers.rs b/linera-base/src/identifiers.rs
index cabbe90626f3..590fb58182a2 100644
--- a/linera-base/src/identifiers.rs
+++ b/linera-base/src/identifiers.rs
@@ -37,7 +37,9 @@ pub enum AccountOwner {
     /// An account owned by a user.
     User(Owner),
     /// An account for an application.
-    Application(ApplicationId),
+    Application(UserApplicationId),
+    /// Chain account.
+    Chain,
 }
 
 /// A system account.
@@ -48,8 +50,7 @@ pub struct Account {
     /// The chain of the account.
     pub chain_id: ChainId,
     /// The owner of the account, or `None` for the chain balance.
-    #[debug(skip_if = Option::is_none)]
-    pub owner: Option<AccountOwner>,
+    pub owner: AccountOwner,
 }
 
 impl Account {
@@ -57,7 +58,7 @@ impl Account {
     pub fn chain(chain_id: ChainId) -> Self {
         Account {
             chain_id,
-            owner: None,
+            owner: AccountOwner::Chain,
         }
     }
 
@@ -65,17 +66,14 @@ impl Account {
     pub fn owner(chain_id: ChainId, owner: impl Into<AccountOwner>) -> Self {
         Account {
             chain_id,
-            owner: Some(owner.into()),
+            owner: owner.into(),
         }
     }
 }
 
 impl Display for Account {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.owner {
-            Some(owner) => write!(f, "{}:{}", self.chain_id, owner),
-            None => write!(f, "{}", self.chain_id),
-        }
+        write!(f, "{}:{}", self.chain_id, self.owner)
     }
 }
 
@@ -306,7 +304,7 @@ pub struct ApplicationId<A = ()> {
 
 /// Alias for `ApplicationId`. Use this alias in the core
 /// protocol where the distinction with the more general enum `GenericApplicationId` matters.
-pub type UserApplicationId<A = ()> = ApplicationId<A>;
+pub type UserApplicationId = ApplicationId<()>;
 
 /// A unique identifier for an application.
 #[derive(
@@ -328,7 +326,7 @@ pub enum GenericApplicationId {
     /// The system application.
     System,
     /// A user application.
-    User(ApplicationId),
+    User(UserApplicationId),
 }
 
 impl GenericApplicationId {
@@ -951,6 +949,7 @@ impl<'de> serde::de::Visitor<'de> for OwnerVisitor {
 enum SerializableAccountOwner {
     User(Owner),
     Application(ApplicationId),
+    Chain,
 }
 
 impl Serialize for AccountOwner {
@@ -961,6 +960,7 @@ impl Serialize for AccountOwner {
             match self {
                 AccountOwner::Application(app_id) => SerializableAccountOwner::Application(*app_id),
                 AccountOwner::User(owner) => SerializableAccountOwner::User(*owner),
+                AccountOwner::Chain => SerializableAccountOwner::Chain,
             }
             .serialize(serializer)
         }
@@ -980,6 +980,7 @@ impl<'de> Deserialize<'de> for AccountOwner {
                     Ok(AccountOwner::Application(app_id))
                 }
                 SerializableAccountOwner::User(owner) => Ok(AccountOwner::User(owner)),
+                SerializableAccountOwner::Chain => Ok(AccountOwner::Chain),
             }
         }
     }
@@ -990,6 +991,7 @@ impl Display for AccountOwner {
         match self {
             AccountOwner::User(owner) => write!(f, "User:{}", owner)?,
             AccountOwner::Application(app_id) => write!(f, "Application:{}", app_id)?,
+            AccountOwner::Chain => write!(f, "Chain")?,
         };
 
         Ok(())
@@ -1008,6 +1010,8 @@ impl FromStr for AccountOwner {
             Ok(AccountOwner::Application(
                 ApplicationId::from_str(app_id).context("Getting ApplicationId should not fail")?,
             ))
+        } else if s.strip_prefix("Chain").is_some() {
+            Ok(AccountOwner::Chain)
         } else {
             Err(anyhow!("Invalid enum! Enum: {}", s))
         }
diff --git a/linera-base/src/unit_tests.rs b/linera-base/src/unit_tests.rs
index 5756286130c4..e2fbb5731470 100644
--- a/linera-base/src/unit_tests.rs
+++ b/linera-base/src/unit_tests.rs
@@ -85,7 +85,7 @@ fn send_message_request_test_case() -> SendMessageRequest<Vec<u8>> {
 fn account_test_case() -> Account {
     Account {
         chain_id: ChainId::root(10),
-        owner: Some(AccountOwner::User(Owner(CryptoHash::test_hash("account")))),
+        owner: AccountOwner::User(Owner(CryptoHash::test_hash("account"))),
     }
 }
 
diff --git a/linera-core/src/chain_worker/state/temporary_changes.rs b/linera-core/src/chain_worker/state/temporary_changes.rs
index 04a8bc984809..77cc392d2c7c 100644
--- a/linera-core/src/chain_worker/state/temporary_changes.rs
+++ b/linera-core/src/chain_worker/state/temporary_changes.rs
@@ -219,9 +219,14 @@ where
         if query.request_committees {
             info.requested_committees = Some(chain.execution_state.system.committees.get().clone());
         }
-        if let Some(owner) = query.request_owner_balance {
-            info.requested_owner_balance =
-                chain.execution_state.system.balances.get(&owner).await?;
+        match query.request_owner_balance {
+            owner @ AccountOwner::Application(_) | owner @ AccountOwner::User(_) => {
+                info.requested_owner_balance =
+                    chain.execution_state.system.balances.get(&owner).await?;
+            }
+            AccountOwner::Chain => {
+                info.requested_owner_balance = Some(*chain.execution_state.system.balance.get());
+            }
         }
         if let Some(next_block_height) = query.test_next_block_height {
             ensure!(
diff --git a/linera-core/src/client/mod.rs b/linera-core/src/client/mod.rs
index feb46bb14433..a70366b074d0 100644
--- a/linera-core/src/client/mod.rs
+++ b/linera-core/src/client/mod.rs
@@ -2260,7 +2260,7 @@ where
     #[instrument(level = "trace", skip(application_id, query))]
     pub async fn query_user_application<A: Abi>(
         &self,
-        application_id: UserApplicationId<A>,
+        application_id: ApplicationId<A>,
         query: &A::Query,
     ) -> Result<QueryOutcome<A::QueryResponse>, ChainClientError> {
         let query = Query::user(application_id, query)?;
@@ -2294,7 +2294,7 @@ where
     /// block.
     #[instrument(level = "trace")]
     pub async fn query_balance(&self) -> Result<Amount, ChainClientError> {
-        let (balance, _) = self.query_balances_with_owner(None).await?;
+        let (balance, _) = self.query_balances_with_owner(AccountOwner::Chain).await?;
         Ok(balance)
     }
 
@@ -2310,7 +2310,7 @@ where
         owner: AccountOwner,
     ) -> Result<Amount, ChainClientError> {
         Ok(self
-            .query_balances_with_owner(Some(owner))
+            .query_balances_with_owner(owner)
             .await?
             .1
             .unwrap_or(Amount::ZERO))
@@ -2325,7 +2325,7 @@ where
     #[instrument(level = "trace", skip(owner))]
     async fn query_balances_with_owner(
         &self,
-        owner: Option<AccountOwner>,
+        owner: AccountOwner,
     ) -> Result<(Amount, Option<Amount>), ChainClientError> {
         let incoming_bundles = self.pending_message_bundles().await?;
         let (previous_block_hash, height, timestamp) = {
@@ -2343,10 +2343,11 @@ where
             operations: Vec::new(),
             previous_block_hash,
             height,
-            authenticated_signer: owner.and_then(|owner| match owner {
+            authenticated_signer: match owner {
                 AccountOwner::User(user) => Some(user),
                 AccountOwner::Application(_) => None,
-            }),
+                AccountOwner::Chain => None, // These should be unreachable?
+            },
             timestamp,
         };
         match self
@@ -2382,7 +2383,7 @@ where
     /// Does not process the inbox or attempt to synchronize with validators.
     #[instrument(level = "trace")]
     pub async fn local_balance(&self) -> Result<Amount, ChainClientError> {
-        let (balance, _) = self.local_balances_with_owner(None).await?;
+        let (balance, _) = self.local_balances_with_owner(AccountOwner::Chain).await?;
         Ok(balance)
     }
 
@@ -2395,7 +2396,7 @@ where
         owner: AccountOwner,
     ) -> Result<Amount, ChainClientError> {
         Ok(self
-            .local_balances_with_owner(Some(owner))
+            .local_balances_with_owner(owner)
             .await?
             .1
             .unwrap_or(Amount::ZERO))
@@ -2407,7 +2408,7 @@ where
     #[instrument(level = "trace", skip(owner))]
     async fn local_balances_with_owner(
         &self,
-        owner: Option<AccountOwner>,
+        owner: AccountOwner,
     ) -> Result<(Amount, Option<Amount>), ChainClientError> {
         let next_block_height = self.next_block_height();
         ensure!(
@@ -2936,7 +2937,7 @@ where
         parameters: &Parameters,
         instantiation_argument: &InstantiationArgument,
         required_application_ids: Vec<UserApplicationId>,
-    ) -> Result<ClientOutcome<(UserApplicationId<A>, ConfirmedBlockCertificate)>, ChainClientError>
+    ) -> Result<ClientOutcome<(ApplicationId<A>, ConfirmedBlockCertificate)>, ChainClientError>
     {
         let instantiation_argument = serde_json::to_vec(instantiation_argument)?;
         let parameters = serde_json::to_vec(parameters)?;
diff --git a/linera-core/src/data_types.rs b/linera-core/src/data_types.rs
index 3c5ad0c2256d..0d93c00e0432 100644
--- a/linera-core/src/data_types.rs
+++ b/linera-core/src/data_types.rs
@@ -71,8 +71,7 @@ pub struct ChainInfoQuery {
     #[debug(skip_if = Option::is_none)]
     pub test_next_block_height: Option<BlockHeight>,
     /// Request the balance of a given [`AccountOwner`].
-    #[debug(skip_if = Option::is_none)]
-    pub request_owner_balance: Option<AccountOwner>,
+    pub request_owner_balance: AccountOwner,
     /// Query the current committees.
     #[debug(skip_if = Not::not)]
     pub request_committees: bool,
@@ -102,7 +101,7 @@ impl ChainInfoQuery {
             chain_id,
             test_next_block_height: None,
             request_committees: false,
-            request_owner_balance: None,
+            request_owner_balance: AccountOwner::Chain,
             request_pending_message_bundles: false,
             request_sent_certificate_hashes_in_range: None,
             request_received_log_excluding_first_n: None,
@@ -123,7 +122,7 @@ impl ChainInfoQuery {
     }
 
     pub fn with_owner_balance(mut self, owner: AccountOwner) -> Self {
-        self.request_owner_balance = Some(owner);
+        self.request_owner_balance = owner;
         self
     }
 
diff --git a/linera-core/src/unit_tests/client_tests.rs b/linera-core/src/unit_tests/client_tests.rs
index c29f843d328f..b7684dc224c5 100644
--- a/linera-core/src/unit_tests/client_tests.rs
+++ b/linera-core/src/unit_tests/client_tests.rs
@@ -195,10 +195,7 @@ where
         Amount::from_tokens(3)
     );
     assert_eq!(
-        receiver
-            .local_balances_with_owner(Some(owner))
-            .await
-            .unwrap(),
+        receiver.local_balances_with_owner(owner).await.unwrap(),
         (Amount::ZERO, Some(Amount::from_tokens(3)))
     );
     assert_eq!(receiver.query_balance().await.unwrap(), Amount::ZERO);
@@ -207,10 +204,7 @@ where
         Amount::from_millis(2999)
     );
     assert_eq!(
-        receiver
-            .query_balances_with_owner(Some(owner))
-            .await
-            .unwrap(),
+        receiver.query_balances_with_owner(owner).await.unwrap(),
         (Amount::ZERO, Some(Amount::from_millis(2999)))
     );
 
diff --git a/linera-core/src/unit_tests/worker_tests.rs b/linera-core/src/unit_tests/worker_tests.rs
index e926fa7134ce..98e50ac30c26 100644
--- a/linera-core/src/unit_tests/worker_tests.rs
+++ b/linera-core/src/unit_tests/worker_tests.rs
@@ -323,7 +323,9 @@ where
                 account.chain_id,
                 MessageKind::Tracked,
                 SystemMessage::Credit {
-                    source: source.map(AccountOwner::User),
+                    source: source
+                        .map(AccountOwner::User)
+                        .unwrap_or(AccountOwner::Chain),
                     target: account.owner,
                     amount,
                 },
@@ -371,16 +373,16 @@ fn direct_outgoing_message(
 
 fn system_credit_message(amount: Amount) -> Message {
     Message::System(SystemMessage::Credit {
-        source: None,
-        target: None,
+        source: AccountOwner::Chain,
+        target: AccountOwner::Chain,
         amount,
     })
 }
 
 fn direct_credit_message(recipient: ChainId, amount: Amount) -> OutgoingMessage {
     let message = SystemMessage::Credit {
-        source: None,
-        target: None,
+        source: AccountOwner::Chain,
+        target: AccountOwner::Chain,
         amount,
     };
     direct_outgoing_message(recipient, MessageKind::Tracked, message)
@@ -2090,14 +2092,14 @@ where
     let sender = Owner::from(sender_key_pair.public());
     let sender_account = Account {
         chain_id: ChainId::root(1),
-        owner: Some(AccountOwner::User(sender)),
+        owner: AccountOwner::User(sender),
     };
 
     let recipient_key_pair = AccountSecretKey::generate();
     let recipient = Owner::from(sender_key_pair.public());
     let recipient_account = Account {
         chain_id: ChainId::root(2),
-        owner: Some(AccountOwner::User(recipient)),
+        owner: AccountOwner::User(recipient),
     };
 
     let (committee, worker) = init_worker_with_chains(
@@ -2152,8 +2154,8 @@ where
                 timestamp: Timestamp::from(0),
                 transaction_index: 0,
                 messages: vec![Message::System(SystemMessage::Credit {
-                    source: None,
-                    target: Some(AccountOwner::User(sender)),
+                    source: AccountOwner::Chain,
+                    target: AccountOwner::User(sender),
                     amount: Amount::from_tokens(5),
                 })
                 .to_posted(0, MessageKind::Tracked)],
@@ -2233,8 +2235,8 @@ where
                     timestamp: Timestamp::from(0),
                     transaction_index: 0,
                     messages: vec![Message::System(SystemMessage::Credit {
-                        source: Some(AccountOwner::User(sender)),
-                        target: Some(AccountOwner::User(recipient)),
+                        source: AccountOwner::User(sender),
+                        target: AccountOwner::User(recipient),
                         amount: Amount::from_tokens(3),
                     })
                     .to_posted(0, MessageKind::Tracked)],
@@ -2249,8 +2251,8 @@ where
                     timestamp: Timestamp::from(0),
                     transaction_index: 0,
                     messages: vec![Message::System(SystemMessage::Credit {
-                        source: Some(AccountOwner::User(sender)),
-                        target: Some(AccountOwner::User(recipient)),
+                        source: AccountOwner::User(sender),
+                        target: AccountOwner::User(recipient),
                         amount: Amount::from_tokens(2),
                     })
                     .to_posted(0, MessageKind::Tracked)],
@@ -2291,8 +2293,8 @@ where
                 timestamp: Timestamp::from(0),
                 transaction_index: 0,
                 messages: vec![Message::System(SystemMessage::Credit {
-                    source: Some(AccountOwner::User(sender)),
-                    target: Some(AccountOwner::User(recipient)),
+                    source: AccountOwner::User(sender),
+                    target: AccountOwner::User(recipient),
                     amount: Amount::from_tokens(3),
                 })
                 .to_posted(0, MessageKind::Bouncing)],
diff --git a/linera-execution/src/execution.rs b/linera-execution/src/execution.rs
index da55c8b64f57..c11197ebaf71 100644
--- a/linera-execution/src/execution.rs
+++ b/linera-execution/src/execution.rs
@@ -401,7 +401,10 @@ where
             kind: MessageKind::Tracked,
             message: SystemMessage::Credit {
                 amount,
-                source: context.authenticated_signer.map(AccountOwner::User),
+                source: context
+                    .authenticated_signer
+                    .map(AccountOwner::User)
+                    .unwrap_or(AccountOwner::Chain),
                 target: account.owner,
             },
         };
diff --git a/linera-execution/src/execution_state_actor.rs b/linera-execution/src/execution_state_actor.rs
index 3ca8e7202951..a2c3403c126c 100644
--- a/linera-execution/src/execution_state_actor.rs
+++ b/linera-execution/src/execution_state_actor.rs
@@ -196,14 +196,13 @@ where
                 application_id,
                 callback,
             } => {
-                let owner = source.owner.ok_or(ExecutionError::OwnerIsNone)?;
                 let mut execution_outcome = RawExecutionOutcome::default();
                 let message = self
                     .system
                     .claim(
                         signer,
                         Some(application_id),
-                        owner,
+                        source.owner,
                         source.chain_id,
                         Recipient::Account(destination),
                         amount,
@@ -551,8 +550,7 @@ pub enum ExecutionRequest {
     },
 
     Transfer {
-        #[debug(skip_if = Option::is_none)]
-        source: Option<AccountOwner>,
+        source: AccountOwner,
         destination: Account,
         amount: Amount,
         #[debug(skip_if = Option::is_none)]
diff --git a/linera-execution/src/lib.rs b/linera-execution/src/lib.rs
index 9f72b25c1974..5ec92de95d6d 100644
--- a/linera-execution/src/lib.rs
+++ b/linera-execution/src/lib.rs
@@ -711,7 +711,7 @@ pub trait ContractRuntime: BaseRuntime {
     /// Transfers amount from source to destination.
     fn transfer(
         &mut self,
-        source: Option<AccountOwner>,
+        source: AccountOwner,
         destination: Account,
         amount: Amount,
     ) -> Result<(), ExecutionError>;
@@ -1028,10 +1028,12 @@ impl<Message> RawOutgoingMessage<Message, Resources> {
 }
 
 impl OperationContext {
+    /// Returns an account for the refund.
+    /// Returns `None` if there is no authenticated signer of the [`OperationContext`].
     fn refund_grant_to(&self) -> Option<Account> {
-        Some(Account {
+        self.authenticated_signer.map(|owner| Account {
             chain_id: self.chain_id,
-            owner: self.authenticated_signer.map(AccountOwner::User),
+            owner: AccountOwner::User(owner),
         })
     }
 
@@ -1176,7 +1178,7 @@ impl Operation {
     /// Creates a new user application operation following the `application_id`'s [`Abi`].
     #[cfg(with_testing)]
     pub fn user<A: Abi>(
-        application_id: UserApplicationId<A>,
+        application_id: ApplicationId<A>,
         operation: &A::Operation,
     ) -> Result<Self, bcs::Error> {
         Self::user_without_abi(application_id.forget_abi(), operation)
@@ -1186,7 +1188,7 @@ impl Operation {
     /// `application_id`.
     #[cfg(with_testing)]
     pub fn user_without_abi(
-        application_id: UserApplicationId<()>,
+        application_id: ApplicationId<()>,
         operation: &impl Serialize,
     ) -> Result<Self, bcs::Error> {
         Ok(Operation::User {
@@ -1234,7 +1236,7 @@ impl Message {
     /// Creates a new user application message assuming that the `message` is valid for the
     /// `application_id`.
     pub fn user<A, M: Serialize>(
-        application_id: UserApplicationId<A>,
+        application_id: ApplicationId<A>,
         message: &M,
     ) -> Result<Self, bcs::Error> {
         let application_id = application_id.forget_abi();
@@ -1299,7 +1301,7 @@ impl Query {
 
     /// Creates a new user application query following the `application_id`'s [`Abi`].
     pub fn user<A: Abi>(
-        application_id: UserApplicationId<A>,
+        application_id: ApplicationId<A>,
         query: &A::Query,
     ) -> Result<Self, serde_json::Error> {
         Self::user_without_abi(application_id.forget_abi(), query)
@@ -1308,7 +1310,7 @@ impl Query {
     /// Creates a new user application query assuming that the `query` is valid for the
     /// `application_id`.
     pub fn user_without_abi(
-        application_id: UserApplicationId<()>,
+        application_id: ApplicationId<()>,
         query: &impl Serialize,
     ) -> Result<Self, serde_json::Error> {
         Ok(Query::User {
diff --git a/linera-execution/src/runtime.rs b/linera-execution/src/runtime.rs
index d1e0a13235cc..1fb5a2d18e67 100644
--- a/linera-execution/src/runtime.rs
+++ b/linera-execution/src/runtime.rs
@@ -1272,7 +1272,7 @@ impl ContractRuntime for ContractSyncRuntimeHandle {
 
     fn transfer(
         &mut self,
-        source: Option<AccountOwner>,
+        source: AccountOwner,
         destination: Account,
         amount: Amount,
     ) -> Result<(), ExecutionError> {
diff --git a/linera-execution/src/system.rs b/linera-execution/src/system.rs
index 35ea03a64a21..3af1132eb566 100644
--- a/linera-execution/src/system.rs
+++ b/linera-execution/src/system.rs
@@ -210,11 +210,9 @@ pub enum SystemMessage {
     /// Credits `amount` units of value to the account `target` -- unless the message is
     /// bouncing, in which case `source` is credited instead.
     Credit {
-        #[debug(skip_if = Option::is_none)]
-        target: Option<AccountOwner>,
+        target: AccountOwner,
         amount: Amount,
-        #[debug(skip_if = Option::is_none)]
-        source: Option<AccountOwner>,
+        source: AccountOwner,
     },
     /// Withdraws `amount` units of value from the account and starts a transfer to credit
     /// the recipient. The message must be properly authenticated. Receiver chains may
@@ -419,7 +417,7 @@ where
                     .transfer(
                         context.authenticated_signer,
                         None,
-                        owner.map(AccountOwner::User),
+                        owner.map(AccountOwner::User).unwrap_or(AccountOwner::Chain),
                         recipient,
                         amount,
                     )
@@ -645,24 +643,22 @@ where
         &mut self,
         authenticated_signer: Option<Owner>,
         authenticated_application_id: Option<UserApplicationId>,
-        source: Option<AccountOwner>,
+        source: AccountOwner,
         recipient: Recipient,
         amount: Amount,
     ) -> Result<Option<RawOutgoingMessage<SystemMessage, Amount>>, ExecutionError> {
         match (source, authenticated_signer, authenticated_application_id) {
-            (Some(AccountOwner::User(owner)), Some(signer), _) => ensure!(
+            (AccountOwner::User(owner), Some(signer), _) => ensure!(
                 signer == owner,
                 ExecutionError::UnauthenticatedTransferOwner
             ),
-            (
-                Some(AccountOwner::Application(account_application)),
-                _,
-                Some(authorized_application),
-            ) => ensure!(
-                account_application == authorized_application,
-                ExecutionError::UnauthenticatedTransferOwner
-            ),
-            (None, Some(signer), _) => ensure!(
+            (AccountOwner::Application(account_application), _, Some(authorized_application)) => {
+                ensure!(
+                    account_application == authorized_application,
+                    ExecutionError::UnauthenticatedTransferOwner
+                )
+            }
+            (AccountOwner::Chain, Some(signer), _) => ensure!(
                 self.ownership.get().verify_owner(&signer),
                 ExecutionError::UnauthenticatedTransferOwner
             ),
@@ -672,7 +668,7 @@ where
             amount > Amount::ZERO,
             ExecutionError::IncorrectTransferAmount
         );
-        self.debit(source.as_ref(), amount).await?;
+        self.debit(&source, amount).await?;
         match recipient {
             Recipient::Account(account) => {
                 let message = RawOutgoingMessage {
@@ -711,6 +707,7 @@ where
                 authenticated_application_id == Some(owner),
                 ExecutionError::UnauthenticatedClaimOwner
             ),
+            AccountOwner::Chain => unreachable!(),
         }
         ensure!(amount > Amount::ZERO, ExecutionError::IncorrectClaimAmount);
 
@@ -730,26 +727,28 @@ where
     /// Debits an [`Amount`] of tokens from an account's balance.
     async fn debit(
         &mut self,
-        account: Option<&AccountOwner>,
+        account: &AccountOwner,
         amount: Amount,
     ) -> Result<(), ExecutionError> {
-        let balance = if let Some(owner) = account {
-            self.balances.get_mut(owner).await?.ok_or_else(|| {
+        let balance = match account {
+            AccountOwner::Chain => self.balance.get_mut(),
+            other => self.balances.get_mut(other).await?.ok_or_else(|| {
                 ExecutionError::InsufficientFunding {
                     balance: Amount::ZERO,
                 }
-            })?
-        } else {
-            self.balance.get_mut()
+            })?,
         };
 
         balance
             .try_sub_assign(amount)
             .map_err(|_| ExecutionError::InsufficientFunding { balance: *balance })?;
 
-        if let Some(owner) = account {
-            if balance.is_zero() {
-                self.balances.remove(owner)?;
+        match account {
+            AccountOwner::Chain => {}
+            other => {
+                if balance.is_zero() {
+                    self.balances.remove(other)?;
+                }
             }
         }
 
@@ -772,12 +771,12 @@ where
             } => {
                 let receiver = if context.is_bouncing { source } else { target };
                 match receiver {
-                    None => {
+                    AccountOwner::Chain => {
                         let new_balance = self.balance.get().saturating_add(amount);
                         self.balance.set(new_balance);
                     }
-                    Some(owner) => {
-                        let balance = self.balances.get_mut_or_default(&owner).await?;
+                    other => {
+                        let balance = self.balances.get_mut_or_default(&other).await?;
                         *balance = balance.saturating_add(amount);
                     }
                 }
@@ -787,7 +786,7 @@ where
                 owner,
                 recipient,
             } => {
-                self.debit(Some(&owner), amount).await?;
+                self.debit(&owner, amount).await?;
                 match recipient {
                     Recipient::Account(account) => {
                         let message = RawOutgoingMessage {
@@ -797,7 +796,7 @@ where
                             kind: MessageKind::Tracked,
                             message: SystemMessage::Credit {
                                 amount,
-                                source: Some(owner),
+                                source: owner,
                                 target: account.owner,
                             },
                         };
@@ -882,7 +881,7 @@ where
                 epoch: config.epoch,
             }
         );
-        self.debit(None, config.balance).await?;
+        self.debit(&AccountOwner::Chain, config.balance).await?;
         let open_chain_message = RawOutgoingMessage {
             destination: Destination::Recipient(child_id),
             authenticated: false,
diff --git a/linera-execution/src/unit_tests/system_tests.rs b/linera-execution/src/unit_tests/system_tests.rs
index 02394494d207..01ebc81501b7 100644
--- a/linera-execution/src/unit_tests/system_tests.rs
+++ b/linera-execution/src/unit_tests/system_tests.rs
@@ -129,7 +129,7 @@ async fn empty_accounts_are_removed() -> anyhow::Result<()> {
     .into_view()
     .await;
 
-    view.system.debit(Some(&owner), amount).await?;
+    view.system.debit(&owner, amount).await?;
 
     assert!(view.system.balances.indices().await?.is_empty());
 
diff --git a/linera-execution/src/wasm/runtime_api.rs b/linera-execution/src/wasm/runtime_api.rs
index b6b755da8830..4b3eaa4c74ce 100644
--- a/linera-execution/src/wasm/runtime_api.rs
+++ b/linera-execution/src/wasm/runtime_api.rs
@@ -471,7 +471,7 @@ where
     /// balance) to `destination`.
     fn transfer(
         caller: &mut Caller,
-        source: Option<AccountOwner>,
+        source: AccountOwner,
         destination: Account,
         amount: Amount,
     ) -> Result<(), RuntimeError> {
diff --git a/linera-execution/tests/contract_runtime_apis.rs b/linera-execution/tests/contract_runtime_apis.rs
index 7611304d7b3d..ad93d9a3fccf 100644
--- a/linera-execution/tests/contract_runtime_apis.rs
+++ b/linera-execution/tests/contract_runtime_apis.rs
@@ -788,25 +788,25 @@ impl TransferTestEndpoint {
     }
 
     /// Returns the [`AccountOwner`] to represent this transfer endpoint as a sender.
-    pub fn sender_account_owner(&self) -> Option<AccountOwner> {
+    pub fn sender_account_owner(&self) -> AccountOwner {
         match self {
-            TransferTestEndpoint::Chain => None,
-            TransferTestEndpoint::User => Some(AccountOwner::User(Self::sender_owner())),
+            TransferTestEndpoint::Chain => AccountOwner::Chain,
+            TransferTestEndpoint::User => AccountOwner::User(Self::sender_owner()),
             TransferTestEndpoint::Application => {
-                Some(AccountOwner::Application(Self::sender_application_id()))
+                AccountOwner::Application(Self::sender_application_id())
             }
         }
     }
 
     /// Returns the [`AccountOwner`] to represent this transfer endpoint as an unauthorized sender.
-    pub fn unauthorized_sender_account_owner(&self) -> Option<AccountOwner> {
+    pub fn unauthorized_sender_account_owner(&self) -> AccountOwner {
         match self {
-            TransferTestEndpoint::Chain => None,
+            TransferTestEndpoint::Chain => AccountOwner::Chain,
             TransferTestEndpoint::User => {
-                Some(AccountOwner::User(Owner(CryptoHash::test_hash("attacker"))))
+                AccountOwner::User(Owner(CryptoHash::test_hash("attacker")))
             }
             TransferTestEndpoint::Application => {
-                Some(AccountOwner::Application(Self::recipient_application_id()))
+                AccountOwner::Application(Self::recipient_application_id())
             }
         }
     }
@@ -832,12 +832,12 @@ impl TransferTestEndpoint {
     }
 
     /// Returns the [`AccountOwner`] to represent this transfer endpoint as a recipient.
-    pub fn recipient_account_owner(&self) -> Option<AccountOwner> {
+    pub fn recipient_account_owner(&self) -> AccountOwner {
         match self {
-            TransferTestEndpoint::Chain => None,
-            TransferTestEndpoint::User => Some(AccountOwner::User(Self::recipient_owner())),
+            TransferTestEndpoint::Chain => AccountOwner::Chain,
+            TransferTestEndpoint::User => AccountOwner::User(Self::recipient_owner()),
             TransferTestEndpoint::Application => {
-                Some(AccountOwner::Application(Self::recipient_application_id()))
+                AccountOwner::Application(Self::recipient_application_id())
             }
         }
     }
@@ -850,8 +850,8 @@ impl TransferTestEndpoint {
         amount: Amount,
     ) -> anyhow::Result<()> {
         let (expected_chain_balance, expected_balances) = match self.recipient_account_owner() {
-            None => (amount, vec![]),
-            Some(account_owner) => (Amount::ZERO, vec![(account_owner, amount)]),
+            AccountOwner::Chain => (amount, vec![]),
+            account_owner => (Amount::ZERO, vec![(account_owner, amount)]),
         };
 
         let balances = system.balances.index_values().await?;
diff --git a/linera-execution/tests/fee_consumption.rs b/linera-execution/tests/fee_consumption.rs
index 396891727b38..13d6678c0e45 100644
--- a/linera-execution/tests/fee_consumption.rs
+++ b/linera-execution/tests/fee_consumption.rs
@@ -187,10 +187,12 @@ async fn test_fee_consumption(
     ));
     application.expect_call(ExpectedCall::default_finalize());
 
-    let refund_grant_to = Some(Account {
-        chain_id: ChainId::root(0),
-        owner: authenticated_signer.map(AccountOwner::User),
-    });
+    let refund_grant_to = authenticated_signer
+        .map(|owner| Account {
+            chain_id: ChainId::root(0),
+            owner: AccountOwner::User(owner),
+        })
+        .or(None);
     let context = MessageContext {
         chain_id: ChainId::root(0),
         is_bouncing: false,
diff --git a/linera-execution/tests/test_execution.rs b/linera-execution/tests/test_execution.rs
index 4da4a6e0e25b..8ade01153007 100644
--- a/linera-execution/tests/test_execution.rs
+++ b/linera-execution/tests/test_execution.rs
@@ -12,7 +12,9 @@ use linera_base::{
         Amount, ApplicationPermissions, Blob, BlockHeight, OracleResponse, Resources,
         SendMessageRequest, Timestamp,
     },
-    identifiers::{Account, ChainDescription, ChainId, Destination, MessageId, Owner},
+    identifiers::{
+        Account, AccountOwner, ChainDescription, ChainId, Destination, MessageId, Owner,
+    },
     ownership::ChainOwnership,
 };
 use linera_execution::{
@@ -627,7 +629,7 @@ async fn test_sending_message_from_finalize() -> anyhow::Result<()> {
 
     let account = Account {
         chain_id: ChainId::root(0),
-        owner: None,
+        owner: AccountOwner::Chain,
     };
 
     let txn_outcome = txn_tracker.into_outcome().unwrap();
@@ -925,7 +927,7 @@ async fn test_simple_message() -> anyhow::Result<()> {
 
     let account = Account {
         chain_id: ChainId::root(0),
-        owner: None,
+        owner: AccountOwner::Chain,
     };
 
     let txn_outcome = txn_tracker.into_outcome().unwrap();
@@ -1008,7 +1010,7 @@ async fn test_message_from_cross_application_call() -> anyhow::Result<()> {
 
     let account = Account {
         chain_id: ChainId::root(0),
-        owner: None,
+        owner: AccountOwner::Chain,
     };
 
     let txn_outcome = txn_tracker.into_outcome().unwrap();
@@ -1102,7 +1104,7 @@ async fn test_message_from_deeper_call() -> anyhow::Result<()> {
 
     let account = Account {
         chain_id: ChainId::root(0),
-        owner: None,
+        owner: AccountOwner::Chain,
     };
     let txn_outcome = txn_tracker.into_outcome().unwrap();
     let mut expected = TransactionTracker::default();
@@ -1235,7 +1237,7 @@ async fn test_multiple_messages_from_different_applications() -> anyhow::Result<
 
     let account = Account {
         chain_id: ChainId::root(0),
-        owner: None,
+        owner: AccountOwner::Chain,
     };
 
     // Return to checking the user application outcomes
@@ -1301,7 +1303,7 @@ async fn test_open_chain() -> anyhow::Result<()> {
         move |runtime, _context, _operation| {
             assert_eq!(runtime.chain_ownership()?, ownership);
             let destination = Account::chain(ChainId::root(2));
-            runtime.transfer(None, destination, Amount::ONE)?;
+            runtime.transfer(AccountOwner::Chain, destination, Amount::ONE)?;
             let id = runtime.application_id()?;
             let application_permissions = ApplicationPermissions::new_single(id);
             let (actual_message_id, chain_id) =
@@ -1498,11 +1500,11 @@ async fn test_message_receipt_spending_chain_balance(
 
     let (application_id, application, blobs) = view.register_mock_application(0).await?;
 
-    let receiver_chain_account = None;
+    let receiver_chain_account = AccountOwner::Chain;
     let sender_chain_id = ChainId::root(2);
     let recipient = Account {
         chain_id: sender_chain_id,
-        owner: None,
+        owner: AccountOwner::Chain,
     };
 
     application.expect_call(ExpectedCall::execute_message(
diff --git a/linera-execution/tests/test_system_execution.rs b/linera-execution/tests/test_system_execution.rs
index 93747e4d0f7e..9a7319dc0e06 100644
--- a/linera-execution/tests/test_system_execution.rs
+++ b/linera-execution/tests/test_system_execution.rs
@@ -6,7 +6,7 @@
 use linera_base::{
     crypto::{AccountSecretKey, CryptoHash},
     data_types::{Amount, BlockHeight, Timestamp},
-    identifiers::{ChainDescription, ChainId, MessageId, Owner},
+    identifiers::{AccountOwner, ChainDescription, ChainId, MessageId, Owner},
     ownership::ChainOwnership,
 };
 use linera_execution::{
@@ -66,8 +66,8 @@ async fn test_simple_system_message() -> anyhow::Result<()> {
     let mut view = state.into_view().await;
     let message = SystemMessage::Credit {
         amount: Amount::from_tokens(4),
-        target: None,
-        source: None,
+        target: AccountOwner::Chain,
+        source: AccountOwner::Chain,
     };
     let context = MessageContext {
         chain_id: ChainId::root(0),
diff --git a/linera-indexer/example/tests/test.rs b/linera-indexer/example/tests/test.rs
index 145fa8c200e0..3823611c31c1 100644
--- a/linera-indexer/example/tests/test.rs
+++ b/linera-indexer/example/tests/test.rs
@@ -9,7 +9,11 @@
 
 use std::{str::FromStr, sync::LazyLock, time::Duration};
 
-use linera_base::{command::resolve_binary, data_types::Amount, identifiers::ChainId};
+use linera_base::{
+    command::resolve_binary,
+    data_types::Amount,
+    identifiers::{Account, ChainId},
+};
 use linera_indexer_graphql_client::{
     indexer::{plugins, state, Plugins, State},
     operations::{get_operation, GetOperation, OperationKey},
@@ -69,10 +73,11 @@ fn indexer_running(child: &mut Child) {
     }
 }
 
-async fn transfer(client: &reqwest::Client, from: ChainId, to: ChainId, amount: &str) {
+async fn transfer(client: &reqwest::Client, from: ChainId, to: Account, amount: &str) {
     let variables = transfer::Variables {
         chain_id: from,
-        recipient: to,
+        recipient_chain: to.chain_id,
+        recipient_account: to.owner,
         amount: Amount::from_str(amount).unwrap(),
     };
     request::<Transfer, _>(client, "http://localhost:8080", variables)
@@ -115,7 +120,7 @@ async fn test_end_to_end_operations_indexer(config: impl LineraNetConfig) {
 
     // making a few transfers
     let chain0 = ChainId::root(0);
-    let chain1 = ChainId::root(1);
+    let chain1 = Account::chain(ChainId::root(1));
     for _ in 0..10 {
         transfer(&req_client, chain0, chain1, "0.1").await;
         linera_base::time::timer::sleep(Duration::from_millis(TRANSFER_DELAY_MILLIS)).await;
diff --git a/linera-rpc/proto/rpc.proto b/linera-rpc/proto/rpc.proto
index 6b7ef1f84fb2..0da981651260 100644
--- a/linera-rpc/proto/rpc.proto
+++ b/linera-rpc/proto/rpc.proto
@@ -190,7 +190,7 @@ message ChainInfoQuery {
   bool request_leader_timeout = 8;
 
   // Query the balance of a given owner.
-  optional AccountOwner request_owner_balance = 9;
+  AccountOwner request_owner_balance = 9;
 
   // Request a signed vote for fallback mode.
   bool request_fallback = 10;
diff --git a/linera-rpc/src/grpc/conversions.rs b/linera-rpc/src/grpc/conversions.rs
index 3c5538bc872e..e6988ed0671f 100644
--- a/linera-rpc/src/grpc/conversions.rs
+++ b/linera-rpc/src/grpc/conversions.rs
@@ -555,10 +555,7 @@ impl TryFrom<api::ChainInfoQuery> for ChainInfoQuery {
 
         Ok(Self {
             request_committees: chain_info_query.request_committees,
-            request_owner_balance: chain_info_query
-                .request_owner_balance
-                .map(TryInto::try_into)
-                .transpose()?,
+            request_owner_balance: try_proto_convert(chain_info_query.request_owner_balance)?,
             request_pending_message_bundles: chain_info_query.request_pending_message_bundles,
             chain_id: try_proto_convert(chain_info_query.chain_id)?,
             request_sent_certificate_hashes_in_range,
@@ -580,10 +577,7 @@ impl TryFrom<ChainInfoQuery> for api::ChainInfoQuery {
             .request_sent_certificate_hashes_in_range
             .map(|range| bincode::serialize(&range))
             .transpose()?;
-        let request_owner_balance = chain_info_query
-            .request_owner_balance
-            .map(|owner| owner.try_into())
-            .transpose()?;
+        let request_owner_balance = Some(chain_info_query.request_owner_balance.try_into()?);
 
         Ok(Self {
             chain_id: Some(chain_info_query.chain_id.into()),
@@ -1109,7 +1103,7 @@ pub mod tests {
             chain_id: ChainId::root(0),
             test_next_block_height: Some(BlockHeight::from(10)),
             request_committees: false,
-            request_owner_balance: None,
+            request_owner_balance: AccountOwner::Chain,
             request_pending_message_bundles: false,
             request_sent_certificate_hashes_in_range: Some(
                 linera_core::data_types::BlockHeightRange {
diff --git a/linera-rpc/tests/snapshots/format__format.yaml.snap b/linera-rpc/tests/snapshots/format__format.yaml.snap
index d0434928ef90..e403f5251b7a 100644
--- a/linera-rpc/tests/snapshots/format__format.yaml.snap
+++ b/linera-rpc/tests/snapshots/format__format.yaml.snap
@@ -7,8 +7,7 @@ Account:
     - chain_id:
         TYPENAME: ChainId
     - owner:
-        OPTION:
-          TYPENAME: AccountOwner
+        TYPENAME: AccountOwner
 AccountOwner:
   ENUM:
     0:
@@ -19,6 +18,8 @@ AccountOwner:
       Application:
         NEWTYPE:
           TYPENAME: ApplicationId
+    2:
+      Chain: UNIT
 AccountPublicKey:
   ENUM:
     0:
@@ -286,8 +287,7 @@ ChainInfoQuery:
         OPTION:
           TYPENAME: BlockHeight
     - request_owner_balance:
-        OPTION:
-          TYPENAME: AccountOwner
+        TYPENAME: AccountOwner
     - request_committees: BOOL
     - request_pending_message_bundles: BOOL
     - request_sent_certificate_hashes_in_range:
@@ -1042,13 +1042,11 @@ SystemMessage:
       Credit:
         STRUCT:
           - target:
-              OPTION:
-                TYPENAME: AccountOwner
+              TYPENAME: AccountOwner
           - amount:
               TYPENAME: Amount
           - source:
-              OPTION:
-                TYPENAME: AccountOwner
+              TYPENAME: AccountOwner
     1:
       Withdraw:
         STRUCT:
diff --git a/linera-sdk/src/base/conversions_from_wit.rs b/linera-sdk/src/base/conversions_from_wit.rs
index 41cdc20dbc03..bc3d9d7b2ee6 100644
--- a/linera-sdk/src/base/conversions_from_wit.rs
+++ b/linera-sdk/src/base/conversions_from_wit.rs
@@ -42,6 +42,7 @@ macro_rules! impl_from_wit {
                     $wit_base_api::AccountOwner::Application(owner) => {
                         AccountOwner::Application(owner.into())
                     }
+                    $wit_base_api::AccountOwner::Chain => AccountOwner::Chain,
                 }
             }
         }
diff --git a/linera-sdk/src/base/conversions_to_wit.rs b/linera-sdk/src/base/conversions_to_wit.rs
index a74758a095f7..ea334e9439d2 100644
--- a/linera-sdk/src/base/conversions_to_wit.rs
+++ b/linera-sdk/src/base/conversions_to_wit.rs
@@ -45,6 +45,7 @@ macro_rules! impl_to_wit {
                     AccountOwner::Application(application_id) => {
                         $wit_base_api::AccountOwner::Application(application_id.into())
                     }
+                    AccountOwner::Chain => $wit_base_api::AccountOwner::Chain,
                 }
             }
         }
diff --git a/linera-sdk/src/contract/conversions_to_wit.rs b/linera-sdk/src/contract/conversions_to_wit.rs
index 6e7e8e5002a7..3af9d85eef84 100644
--- a/linera-sdk/src/contract/conversions_to_wit.rs
+++ b/linera-sdk/src/contract/conversions_to_wit.rs
@@ -58,7 +58,7 @@ impl From<Account> for wit_contract_api::Account {
     fn from(account: Account) -> Self {
         wit_contract_api::Account {
             chain_id: account.chain_id.into(),
-            owner: account.owner.map(|owner| owner.into()),
+            owner: account.owner.into(),
         }
     }
 }
@@ -70,6 +70,7 @@ impl From<AccountOwner> for wit_contract_api::AccountOwner {
             AccountOwner::Application(application_id) => {
                 wit_contract_api::AccountOwner::Application(application_id.into())
             }
+            AccountOwner::Chain => wit_contract_api::AccountOwner::Chain,
         }
     }
 }
diff --git a/linera-sdk/src/contract/runtime.rs b/linera-sdk/src/contract/runtime.rs
index fc5b0509732f..4db3e65ab3b9 100644
--- a/linera-sdk/src/contract/runtime.rs
+++ b/linera-sdk/src/contract/runtime.rs
@@ -231,12 +231,8 @@ where
 
     /// Transfers an `amount` of native tokens from `source` owner account (or the current chain's
     /// balance) to `destination`.
-    pub fn transfer(&mut self, source: Option<AccountOwner>, destination: Account, amount: Amount) {
-        contract_wit::transfer(
-            source.map(|source| source.into()),
-            destination.into(),
-            amount.into(),
-        )
+    pub fn transfer(&mut self, source: AccountOwner, destination: Account, amount: Amount) {
+        contract_wit::transfer(source.into(), destination.into(), amount.into())
     }
 
     /// Claims an `amount` of native tokens from a `source` account to a `destination` account.
diff --git a/linera-sdk/src/contract/test_runtime.rs b/linera-sdk/src/contract/test_runtime.rs
index 08fefa4677c8..6cacc8b64d2e 100644
--- a/linera-sdk/src/contract/test_runtime.rs
+++ b/linera-sdk/src/contract/test_runtime.rs
@@ -499,7 +499,7 @@ where
 
     /// Transfers an `amount` of native tokens from `source` owner account (or the current chain's
     /// balance) to `destination`.
-    pub fn transfer(&mut self, source: Option<AccountOwner>, destination: Account, amount: Amount) {
+    pub fn transfer(&mut self, source: AccountOwner, destination: Account, amount: Amount) {
         self.debit(source, amount);
 
         if Some(destination.chain_id) == self.chain_id {
@@ -514,10 +514,10 @@ where
 
     /// Debits an `amount` of native tokens from a `source` owner account (or the current
     /// chain's balance).
-    fn debit(&mut self, source: Option<AccountOwner>, amount: Amount) {
+    fn debit(&mut self, source: AccountOwner, amount: Amount) {
         let source_balance = match source {
-            Some(owner) => self.owner_balance_mut(owner),
-            None => self.chain_balance_mut(),
+            AccountOwner::Application(_) | AccountOwner::User(_) => self.owner_balance_mut(source),
+            AccountOwner::Chain => self.chain_balance_mut(),
         };
 
         *source_balance = source_balance
@@ -527,10 +527,12 @@ where
 
     /// Credits an `amount` of native tokens into a `destination` owner account (or the
     /// current chain's balance).
-    fn credit(&mut self, destination: Option<AccountOwner>, amount: Amount) {
+    fn credit(&mut self, destination: AccountOwner, amount: Amount) {
         let destination_balance = match destination {
-            Some(owner) => self.owner_balance_mut(owner),
-            None => self.chain_balance_mut(),
+            owner @ AccountOwner::Application(_) | owner @ AccountOwner::User(_) => {
+                self.owner_balance_mut(owner)
+            }
+            AccountOwner::Chain => self.chain_balance_mut(),
         };
 
         *destination_balance = destination_balance
diff --git a/linera-sdk/wit/base-runtime-api.wit b/linera-sdk/wit/base-runtime-api.wit
index 82d5440a4ef5..a0336784eaf1 100644
--- a/linera-sdk/wit/base-runtime-api.wit
+++ b/linera-sdk/wit/base-runtime-api.wit
@@ -33,6 +33,7 @@ interface base-runtime-api {
     variant account-owner {
         user(owner),
         application(application-id),
+        chain,
     }
 
     record amount {
diff --git a/linera-sdk/wit/contract-runtime-api.wit b/linera-sdk/wit/contract-runtime-api.wit
index 079f74fde0da..55309e1181a7 100644
--- a/linera-sdk/wit/contract-runtime-api.wit
+++ b/linera-sdk/wit/contract-runtime-api.wit
@@ -8,7 +8,7 @@ interface contract-runtime-api {
     send-message: func(message: send-message-request);
     subscribe: func(chain: chain-id, channel: channel-name);
     unsubscribe: func(chain: chain-id, channel: channel-name);
-    transfer: func(source: option<account-owner>, destination: account, amount: amount);
+    transfer: func(source: account-owner, destination: account, amount: amount);
     claim: func(source: account, destination: account, amount: amount);
     open-chain: func(chain-ownership: chain-ownership, application-permissions: application-permissions, balance: amount) -> tuple<message-id, chain-id>;
     close-chain: func() -> result<tuple<>, close-chain-error>;
@@ -23,12 +23,13 @@ interface contract-runtime-api {
 
     record account {
         chain-id: chain-id,
-        owner: option<account-owner>,
+        owner: account-owner,
     }
 
     variant account-owner {
         user(owner),
         application(application-id),
+        chain,
     }
 
     record amount {
diff --git a/linera-service-graphql-client/gql/service_requests.graphql b/linera-service-graphql-client/gql/service_requests.graphql
index 85fe05b830e9..d6374ff1a44a 100644
--- a/linera-service-graphql-client/gql/service_requests.graphql
+++ b/linera-service-graphql-client/gql/service_requests.graphql
@@ -358,6 +358,6 @@ subscription Notifications($chainId: ChainId!) {
   notifications(chainId: $chainId)
 }
 
-mutation Transfer($chainId: ChainId!, $recipient: ChainId!, $amount: Amount!) {
-  transfer(chainId: $chainId, recipient: { Account: { chain_id: $recipient } }, amount: $amount)
+mutation Transfer($chainId: ChainId!, $recipient_chain: ChainId!, $recipient_account: AccountOwner!, $amount: Amount!) {
+  transfer(chainId: $chainId, recipient: { Account: { chain_id: $recipient_chain, owner: $recipient_account } }, amount: $amount)
 }
diff --git a/linera-service-graphql-client/src/service.rs b/linera-service-graphql-client/src/service.rs
index 4a6ac8e0d15d..de772050998f 100644
--- a/linera-service-graphql-client/src/service.rs
+++ b/linera-service-graphql-client/src/service.rs
@@ -6,8 +6,8 @@ use linera_base::{
     crypto::CryptoHash,
     data_types::{Amount, Blob, BlockHeight, OracleResponse, Round, Timestamp},
     identifiers::{
-        Account, BlobId, ChainDescription, ChainId, ChannelName, Destination, GenericApplicationId,
-        Owner, StreamName,
+        Account, AccountOwner, BlobId, ChainDescription, ChainId, ChannelName, Destination,
+        GenericApplicationId, Owner, StreamName,
     },
 };
 
diff --git a/linera-service-graphql-client/tests/test.rs b/linera-service-graphql-client/tests/test.rs
index c71d99413a60..6416fede9cf3 100644
--- a/linera-service-graphql-client/tests/test.rs
+++ b/linera-service-graphql-client/tests/test.rs
@@ -10,7 +10,11 @@
 use std::{collections::BTreeMap, str::FromStr, sync::LazyLock, time::Duration};
 
 use fungible::{FungibleTokenAbi, InitialState};
-use linera_base::{data_types::Amount, identifiers::ChainId, vm::VmRuntime};
+use linera_base::{
+    data_types::Amount,
+    identifiers::{Account, ChainId},
+    vm::VmRuntime,
+};
 use linera_service::cli_wrappers::{
     local_net::{Database, LocalNetConfig, ProcessInbox},
     LineraNet, LineraNetConfig, Network,
@@ -31,10 +35,11 @@ fn reqwest_client() -> reqwest::Client {
         .unwrap()
 }
 
-async fn transfer(client: &reqwest::Client, url: &str, from: ChainId, to: ChainId, amount: &str) {
+async fn transfer(client: &reqwest::Client, url: &str, from: ChainId, to: Account, amount: &str) {
     let variables = transfer::Variables {
         chain_id: from,
-        recipient: to,
+        recipient_chain: to.chain_id,
+        recipient_account: to.owner,
         amount: Amount::from_str(amount).unwrap(),
     };
     request::<Transfer, _>(client, url, variables)
@@ -86,7 +91,7 @@ async fn test_end_to_end_queries(config: impl LineraNetConfig) {
 
     // sending a few transfers
     let chain0 = ChainId::root(0);
-    let chain1 = ChainId::root(1);
+    let chain1 = Account::chain(ChainId::root(1));
     for _ in 0..10 {
         transfer(req_client, url, chain0, chain1, "0.1").await;
     }
diff --git a/linera-service/benches/transfers.rs b/linera-service/benches/transfers.rs
index f3ce350013b1..483df632184b 100644
--- a/linera-service/benches/transfers.rs
+++ b/linera-service/benches/transfers.rs
@@ -80,7 +80,7 @@ async fn setup_native_token_balances(
     for chain in &chains {
         let recipient = Recipient::Account(Account {
             chain_id: chain.id(),
-            owner: Some(chain.public_key().into()),
+            owner: chain.public_key().into(),
         });
 
         // TODO: Support benchmarking chains with multiple owner accounts
@@ -110,7 +110,7 @@ fn prepare_transfers(
         .iter()
         .map(|chain| Account {
             chain_id: chain.id(),
-            owner: Some(chain.public_key().into()),
+            owner: chain.public_key().into(),
         })
         .collect::<Vec<_>>();
 
diff --git a/linera-service/src/linera/main.rs b/linera-service/src/linera/main.rs
index 77abb0bd302d..6e1a7cee036e 100644
--- a/linera-service/src/linera/main.rs
+++ b/linera-service/src/linera/main.rs
@@ -102,11 +102,11 @@ impl Runnable for Job {
             } => {
                 let chain_client = context.make_chain_client(sender.chain_id)?;
                 let owner = match sender.owner {
-                    Some(AccountOwner::User(owner)) => Some(owner),
-                    Some(AccountOwner::Application(_)) => {
+                    AccountOwner::User(owner) => Some(owner),
+                    AccountOwner::Application(_) => {
                         bail!("Can't transfer from an application account")
                     }
-                    None => None,
+                    AccountOwner::Chain => None,
                 };
                 info!(
                     "Starting transfer of {} native tokens from {} to {}",
@@ -288,8 +288,10 @@ impl Runnable for Job {
                 info!("Reading the balance of {} from the local state", account);
                 let time_start = Instant::now();
                 let balance = match account.owner {
-                    Some(owner) => chain_client.local_owner_balance(owner).await?,
-                    None => chain_client.local_balance().await?,
+                    AccountOwner::User(_) | AccountOwner::Application(_) => {
+                        chain_client.local_owner_balance(account.owner).await?
+                    }
+                    AccountOwner::Chain => chain_client.local_balance().await?,
                 };
                 let time_total = time_start.elapsed();
                 info!("Local balance obtained after {} ms", time_total.as_millis());
@@ -305,8 +307,10 @@ impl Runnable for Job {
                 );
                 let time_start = Instant::now();
                 let balance = match account.owner {
-                    Some(owner) => chain_client.query_owner_balance(owner).await?,
-                    None => chain_client.query_balance().await?,
+                    AccountOwner::User(_) | AccountOwner::Application(_) => {
+                        chain_client.query_owner_balance(account.owner).await?
+                    }
+                    AccountOwner::Chain => chain_client.query_balance().await?,
                 };
                 let time_total = time_start.elapsed();
                 info!("Balance obtained after {} ms", time_total.as_millis());
@@ -321,8 +325,10 @@ impl Runnable for Job {
                 let time_start = Instant::now();
                 chain_client.synchronize_from_validators().await?;
                 let result = match account.owner {
-                    Some(owner) => chain_client.query_owner_balance(owner).await,
-                    None => chain_client.query_balance().await,
+                    AccountOwner::User(_) | AccountOwner::Application(_) => {
+                        chain_client.query_owner_balance(account.owner).await
+                    }
+                    AccountOwner::Chain => chain_client.query_balance().await,
                 };
                 context.update_wallet_from_client(&chain_client).await?;
                 let balance = result.context("Failed to synchronize from validators")?;