diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/TestEngine.cs b/src/Microsoft.TestPlatform.CrossPlatEngine/TestEngine.cs
index 5e61617f1a..08a2a113d5 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/TestEngine.cs
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/TestEngine.cs
@@ -35,25 +35,31 @@ namespace Microsoft.VisualStudio.TestPlatform.CrossPlatEngine;
 public class TestEngine : ITestEngine
 {
     private readonly ITestRuntimeProviderManager _testHostProviderManager;
-    private ITestExtensionManager _testExtensionManager;
     private readonly IProcessHelper _processHelper;
+    private readonly IEnvironment _environment;
+
+    private ITestExtensionManager _testExtensionManager;
 
-    public TestEngine() : this(TestRuntimeProviderManager.Instance, new ProcessHelper())
+    public TestEngine()
+        : this(TestRuntimeProviderManager.Instance, new ProcessHelper())
     {
     }
 
     protected internal TestEngine(
         TestRuntimeProviderManager testHostProviderManager,
-        IProcessHelper processHelper) : this((ITestRuntimeProviderManager)testHostProviderManager, processHelper)
+        IProcessHelper processHelper)
+        : this(testHostProviderManager, processHelper, new PlatformEnvironment())
     {
     }
 
     internal TestEngine(
         ITestRuntimeProviderManager testHostProviderManager,
-        IProcessHelper processHelper)
+        IProcessHelper processHelper,
+        IEnvironment environment)
     {
         _testHostProviderManager = testHostProviderManager;
         _processHelper = processHelper;
+        _environment = environment;
     }
 
     #region ITestEngine implementation
@@ -492,15 +498,21 @@ private int VerifyParallelSettingAndCalculateParallelLevel(
             // Check the user parallel setting.
             int userParallelSetting = RunSettingsUtilities.GetMaxCpuCount(runSettings);
             parallelLevelToUse = userParallelSetting == 0
-                // TODO: use environment helper so we can control this from tests.
-                ? Environment.ProcessorCount
+                ? _environment.ProcessorCount
                 : userParallelSetting;
-            var enableParallel = parallelLevelToUse > 1;
 
             EqtTrace.Verbose(
                 "TestEngine: Initializing Parallel Execution as MaxCpuCount is set to: {0}",
                 parallelLevelToUse);
 
+            // TODO: EXPERIMENTAL FEATURE - will need to be removed or strengthen/tested.
+            // A negative value is used to indicate that the value should be used as a percentage of the number of cores.
+            if (parallelLevelToUse < 0)
+            {
+                parallelLevelToUse = (int)Math.Max(1, Math.Round((double)-parallelLevelToUse * _environment.ProcessorCount / 100.0, MidpointRounding.AwayFromZero));
+            }
+
+            var enableParallel = parallelLevelToUse > 1;
             // Verify if the number of sources is less than user setting of parallel.
             // We should use number of sources as the parallel level, if sources count is less
             // than parallel level.
diff --git a/src/Microsoft.TestPlatform.PlatformAbstractions/Interfaces/System/IEnvironment.cs b/src/Microsoft.TestPlatform.PlatformAbstractions/Interfaces/System/IEnvironment.cs
index 6e3e745cb1..7af77732e5 100644
--- a/src/Microsoft.TestPlatform.PlatformAbstractions/Interfaces/System/IEnvironment.cs
+++ b/src/Microsoft.TestPlatform.PlatformAbstractions/Interfaces/System/IEnvironment.cs
@@ -34,4 +34,7 @@ public interface IEnvironment
     /// </summary>
     /// <returns>Returns the thread Id</returns>
     int GetCurrentManagedThreadId();
+
+    /// <inheritdoc cref="System.Environment.ProcessorCount"/>
+    int ProcessorCount { get; }
 }
diff --git a/src/Microsoft.TestPlatform.PlatformAbstractions/PublicAPI/PublicAPI.Shipped.txt b/src/Microsoft.TestPlatform.PlatformAbstractions/PublicAPI/PublicAPI.Shipped.txt
index 9a6ec487a0..759b9e899a 100644
--- a/src/Microsoft.TestPlatform.PlatformAbstractions/PublicAPI/PublicAPI.Shipped.txt
+++ b/src/Microsoft.TestPlatform.PlatformAbstractions/PublicAPI/PublicAPI.Shipped.txt
@@ -36,6 +36,7 @@ Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IAssemblyRes
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IAssemblyResolver.AssemblyResolve -> Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.AssemblyResolveEventHandler?
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IEnvironment
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IEnvironment.Architecture.get -> Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformArchitecture
+Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IEnvironment.ProcessorCount.get -> int
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IEnvironment.Exit(int exitcode) -> void
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IEnvironment.GetCurrentManagedThreadId() -> int
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.Interfaces.IEnvironment.OperatingSystem.get -> Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformOperatingSystem
@@ -79,6 +80,7 @@ Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformAssemblyResolve
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformAssemblyResolver.PlatformAssemblyResolver() -> void
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformEnvironment
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformEnvironment.Architecture.get -> Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformArchitecture
+Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformEnvironment.ProcessorCount.get -> int
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformEnvironment.Exit(int exitcode) -> void
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformEnvironment.GetCurrentManagedThreadId() -> int
 Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformEnvironment.OperatingSystem.get -> Microsoft.VisualStudio.TestPlatform.PlatformAbstractions.PlatformOperatingSystem
diff --git a/src/Microsoft.TestPlatform.PlatformAbstractions/net451/System/PlatformEnvironment.cs b/src/Microsoft.TestPlatform.PlatformAbstractions/net451/System/PlatformEnvironment.cs
index 202263d19f..09fb1ea528 100644
--- a/src/Microsoft.TestPlatform.PlatformAbstractions/net451/System/PlatformEnvironment.cs
+++ b/src/Microsoft.TestPlatform.PlatformAbstractions/net451/System/PlatformEnvironment.cs
@@ -73,6 +73,9 @@ public PlatformOperatingSystem OperatingSystem
     /// <inheritdoc />
     public string OperatingSystemVersion => Environment.OSVersion.ToString();
 
+    /// <inheritdoc />
+    public int ProcessorCount => Environment.ProcessorCount;
+
     /// <inheritdoc />
     public void Exit(int exitcode)
     {
diff --git a/src/Microsoft.TestPlatform.PlatformAbstractions/netcore/System/PlatformEnvironment.cs b/src/Microsoft.TestPlatform.PlatformAbstractions/netcore/System/PlatformEnvironment.cs
index 61e73c0455..10d4a61570 100644
--- a/src/Microsoft.TestPlatform.PlatformAbstractions/netcore/System/PlatformEnvironment.cs
+++ b/src/Microsoft.TestPlatform.PlatformAbstractions/netcore/System/PlatformEnvironment.cs
@@ -56,6 +56,9 @@ public string OperatingSystemVersion
         }
     }
 
+    /// <inheritdoc />
+    public int ProcessorCount => Environment.ProcessorCount;
+
     /// <inheritdoc />
     public void Exit(int exitcode)
     {
diff --git a/src/Microsoft.TestPlatform.PlatformAbstractions/netstandard/System/PlatformEnvironment.cs b/src/Microsoft.TestPlatform.PlatformAbstractions/netstandard/System/PlatformEnvironment.cs
index 61d274b2bd..377cf4b4d4 100644
--- a/src/Microsoft.TestPlatform.PlatformAbstractions/netstandard/System/PlatformEnvironment.cs
+++ b/src/Microsoft.TestPlatform.PlatformAbstractions/netstandard/System/PlatformEnvironment.cs
@@ -39,6 +39,9 @@ public string OperatingSystemVersion
         }
     }
 
+    /// <inheritdoc />
+    public int ProcessorCount => throw new NotImplementedException();
+
     /// <inheritdoc />
     public void Exit(int exitcode)
     {
diff --git a/src/Microsoft.TestPlatform.PlatformAbstractions/uap10.0/System/PlatformEnvironment.cs b/src/Microsoft.TestPlatform.PlatformAbstractions/uap10.0/System/PlatformEnvironment.cs
index 3be2617a80..9c53b9b678 100644
--- a/src/Microsoft.TestPlatform.PlatformAbstractions/uap10.0/System/PlatformEnvironment.cs
+++ b/src/Microsoft.TestPlatform.PlatformAbstractions/uap10.0/System/PlatformEnvironment.cs
@@ -33,6 +33,9 @@ public PlatformOperatingSystem OperatingSystem
     /// <inheritdoc />
     public string OperatingSystemVersion => RuntimeInformation.OSDescription;
 
+    /// <inheritdoc />
+    public int ProcessorCount => Environment.ProcessorCount;
+
     /// <inheritdoc />
     public void Exit(int exitcode)
     {
diff --git a/test/vstest.ProgrammerTests/Fakes/FakeEnvironment.cs b/test/vstest.ProgrammerTests/Fakes/FakeEnvironment.cs
index ea82d8501b..415c42f5b9 100644
--- a/test/vstest.ProgrammerTests/Fakes/FakeEnvironment.cs
+++ b/test/vstest.ProgrammerTests/Fakes/FakeEnvironment.cs
@@ -16,6 +16,8 @@ internal class FakeEnvironment : IEnvironment
 
     public string OperatingSystemVersion => _environment.OperatingSystemVersion;
 
+    public int ProcessorCount => _environment.ProcessorCount;
+
     public void Exit(int exitcode) => _environment.Exit(exitcode);
 
     public int GetCurrentManagedThreadId() => _environment.GetCurrentManagedThreadId();
diff --git a/test/vstest.ProgrammerTests/Fakes/Fixture.cs b/test/vstest.ProgrammerTests/Fakes/Fixture.cs
index 60a38bfc35..afddd891d9 100644
--- a/test/vstest.ProgrammerTests/Fakes/Fixture.cs
+++ b/test/vstest.ProgrammerTests/Fakes/Fixture.cs
@@ -107,7 +107,7 @@ internal TestRequestManagerTestHelper BuildTestRequestManager(
             throw new InvalidOperationException("There are runtime providers registered for FakeTestRuntimeProviderManager.");
 
 
-        TestEngine = new TestEngine(TestRuntimeProviderManager, ProcessHelper);
+        TestEngine = new TestEngine(TestRuntimeProviderManager, ProcessHelper, Environment);
         TestPlatform = new TestPlatform(TestEngine, FileHelper, TestRuntimeProviderManager);
 
         TestRunResultAggregator = new TestRunResultAggregator();