diff --git a/.circleci/config.yml b/.circleci/config.yml
index c609a04a57..9ccc0a09c2 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -25,18 +25,12 @@ commands:
       - run:
           name: Run tests
           command: |
+            mkdir -p test-reports
             . /opt/conda/etc/profile.d/conda.sh
             conda activate esmvaltool
             flake8 -j 4
-            pytest -n 4 -m "not sequential" --junitxml=report-1.xml
-            pytest -n 0 -m "sequential" --cov-append --junitxml=report-2.xml
+            pytest -n 4 --junitxml=test-reports/report.xml
             esmvaltool version
-      - run:
-          name: Merge test reports
-          command: |
-            pip install junitparser
-            mkdir -p test-reports
-            junitparser merge report-*.xml test-reports/report.xml
       - store_test_results:
           path: test-reports/
       - store_artifacts:
diff --git a/.github/workflows/create-condalock-file.yml b/.github/workflows/create-condalock-file.yml
index 80516c9c26..1f932e592b 100644
--- a/.github/workflows/create-condalock-file.yml
+++ b/.github/workflows/create-condalock-file.yml
@@ -66,9 +66,7 @@ jobs:
       - shell: bash -l {0}
         run: flake8
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential"
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation"
       # Automated PR
       # see https://github.com/marketplace/actions/create-pull-request
       - name: Create Automated PR if conda lock file has changed
diff --git a/.github/workflows/install-from-condalock-file.yml b/.github/workflows/install-from-condalock-file.yml
index ec326ed96c..d4579f8537 100644
--- a/.github/workflows/install-from-condalock-file.yml
+++ b/.github/workflows/install-from-condalock-file.yml
@@ -61,9 +61,7 @@ jobs:
       - shell: bash -l {0}
         run: flake8
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential"
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation"
       - name: Upload artifacts
         if: ${{ always() }}  # upload artifacts even if fail
         uses: actions/upload-artifact@v2
diff --git a/.github/workflows/run-tests-comment.yml b/.github/workflows/run-tests-comment.yml
index e9790badec..d5342971a7 100644
--- a/.github/workflows/run-tests-comment.yml
+++ b/.github/workflows/run-tests-comment.yml
@@ -36,9 +36,7 @@ jobs:
       - shell: bash -l {0}
         run: flake8
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential" 2>&1 | tee test_linux_artifacts_python_${{ matrix.python-version }}/test_report.txt
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation" 2>&1 | tee test_linux_artifacts_python_${{ matrix.python-version }}/test_report.txt
       - name: Upload artifacts
         if: ${{ always() }}  # upload artifacts even if fail
         uses: actions/upload-artifact@v2
@@ -77,9 +75,7 @@ jobs:
       - shell: bash -l {0}
         run: flake8
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential" 2>&1 | tee test_osx_artifacts_python_${{ matrix.python-version }}/test_report.txt
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation" 2>&1 | tee test_osx_artifacts_python_${{ matrix.python-version }}/test_report.txt
       - name: Upload artifacts
         if: ${{ always() }}  # upload artifacts even if fail
         uses: actions/upload-artifact@v2
diff --git a/.github/workflows/run-tests-monitor.yml b/.github/workflows/run-tests-monitor.yml
index 6ab81fa704..b0abaf15d6 100644
--- a/.github/workflows/run-tests-monitor.yml
+++ b/.github/workflows/run-tests-monitor.yml
@@ -43,11 +43,7 @@ jobs:
       - shell: bash -l {0}
         run: pip install -e .[develop] 2>&1 | tee test_linux_artifacts_python_${{ matrix.python-version }}/install.txt
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential" --db ../.pymon 2>&1 | tee test_linux_artifacts_python_${{ matrix.python-version }}/test_report.txt
-      - shell: bash -l {0}
-        run: python tests/parse_pymon.py
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation" --db ../.pymon 2>&1 | tee test_linux_artifacts_python_${{ matrix.python-version }}/test_report.txt
       - shell: bash -l {0}
         run: python tests/parse_pymon.py
       - name: Upload artifacts
@@ -87,11 +83,7 @@ jobs:
       - shell: bash -l {0}
         run: pip install -e .[develop] 2>&1 | tee test_osx_artifacts_python_${{ matrix.python-version }}/install.txt
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential" --db ../.pymon 2>&1 | tee test_osx_artifacts_python_${{ matrix.python-version }}/test_report.txt
-      - shell: bash -l {0}
-        run: python tests/parse_pymon.py
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation" --db ../.pymon 2>&1 | tee test_osx_artifacts_python_${{ matrix.python-version }}/test_report.txt
       - shell: bash -l {0}
         run: python tests/parse_pymon.py
       - name: Upload artifacts
diff --git a/.github/workflows/run-tests.yml b/.github/workflows/run-tests.yml
index a9322fe9e8..68068bff9c 100644
--- a/.github/workflows/run-tests.yml
+++ b/.github/workflows/run-tests.yml
@@ -60,9 +60,7 @@ jobs:
       - shell: bash -l {0}
         run: flake8
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential" 2>&1 | tee test_linux_artifacts_python_${{ matrix.python-version }}/test_report.txt
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation" 2>&1 | tee test_linux_artifacts_python_${{ matrix.python-version }}/test_report.txt
       - name: Upload artifacts
         if: ${{ always() }}  # upload artifacts even if fail
         uses: actions/upload-artifact@v2
@@ -100,9 +98,7 @@ jobs:
       - shell: bash -l {0}
         run: flake8
       - shell: bash -l {0}
-        run: pytest -n 2 -m "not installation and not sequential" 2>&1 | tee test_osx_artifacts_python_${{ matrix.python-version }}/test_report.txt
-      - shell: bash -l {0}
-        run: pytest -n 0 -m "sequential"
+        run: pytest -n 2 -m "not installation" 2>&1 | tee test_osx_artifacts_python_${{ matrix.python-version }}/test_report.txt
       - name: Upload artifacts
         if: ${{ always() }}  # upload artifacts even if fail
         uses: actions/upload-artifact@v2
diff --git a/setup.cfg b/setup.cfg
index 7fb5f9a5cf..6410153665 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -13,7 +13,6 @@ log_level = WARNING
 markers =
     installation: Test requires installation of dependencies
     use_sample_data: Run functional tests using real data
-    sequential: Run these tests sequentially, see https://github.com/ESMValGroup/ESMValCore/issues/644
 
 [flake8]
 exclude =
diff --git a/tests/integration/cmor/_fixes/test_common.py b/tests/integration/cmor/_fixes/test_common.py
index ff7e42a3e8..3a8bce5505 100644
--- a/tests/integration/cmor/_fixes/test_common.py
+++ b/tests/integration/cmor/_fixes/test_common.py
@@ -84,7 +84,6 @@ def hybrid_pressure_coord_fix_metadata(nc_path, short_name, fix):
     return var_names
 
 
-@pytest.mark.sequential
 def test_cl_hybrid_pressure_coord_fix_metadata_with_a(test_data_path):
     """Test ``fix_metadata`` for ``cl``."""
     vardef = get_var_info('CMIP6', 'Amon', 'cl')
@@ -94,7 +93,6 @@ def test_cl_hybrid_pressure_coord_fix_metadata_with_a(test_data_path):
     assert 'a_bnds' in var_names
 
 
-@pytest.mark.sequential
 def test_cl_hybrid_pressure_coord_fix_metadata_with_ap(test_data_path):
     """Test ``fix_metadata`` for ``cl``."""
     vardef = get_var_info('CMIP6', 'Amon', 'cl')
@@ -162,7 +160,6 @@ def hybrid_height_coord_fix_metadata(nc_path, short_name, fix):
     assert air_pressure_coord.units == 'Pa'
 
 
-@pytest.mark.sequential
 def test_cl_hybrid_height_coord_fix_metadata(test_data_path):
     """Test ``fix_metadata`` for ``cl``."""
     vardef = get_var_info('CMIP6', 'Amon', 'cl')
diff --git a/tests/integration/cmor/_fixes/test_shared.py b/tests/integration/cmor/_fixes/test_shared.py
index 5029c9306f..e82005f595 100644
--- a/tests/integration/cmor/_fixes/test_shared.py
+++ b/tests/integration/cmor/_fixes/test_shared.py
@@ -27,7 +27,6 @@
 )
 
 
-@pytest.mark.sequential
 def test_altitude_to_pressure_func():
     """Test altitude to pressure function."""
     func = get_altitude_to_pressure_func()
@@ -42,7 +41,6 @@ def test_altitude_to_pressure_func():
                                [101325.0, 100129.0])
 
 
-@pytest.mark.sequential
 def test_pressure_to_altitude_func():
     """Test pressure to altitude function."""
     func = get_pressure_to_altitude_func()
@@ -71,7 +69,6 @@ def test_pressure_to_altitude_func():
 ]
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('coord_dict,output', TEST_ADD_AUX_COORDS_FROM_CUBES)
 def test_add_aux_coords_from_cubes(coord_dict, output):
     """Test extraction of auxiliary coordinates from cubes."""
@@ -132,7 +129,6 @@ def test_add_aux_coords_from_cubes(coord_dict, output):
 ]
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube,output', TEST_ADD_PLEV_FROM_ALTITUDE)
 def test_add_plev_from_altitude(cube, output):
     """Test adding of pressure level coordinate."""
@@ -170,7 +166,6 @@ def test_add_plev_from_altitude(cube, output):
 ]
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube,output', TEST_ADD_ALTITUDE_FROM_PLEV)
 def test_add_altitude_from_plev(cube, output):
     """Test adding of altitude coordinate."""
@@ -216,7 +211,6 @@ def test_add_altitude_from_plev(cube, output):
 TEST_ADD_SCALAR_COORD_NO_VALS = [CUBE_1.copy(), CUBE_2.copy()]
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube_in,depth', TEST_ADD_SCALAR_COORD)
 def test_add_scalar_depth_coord(cube_in, depth):
     """Test adding of scalar depth coordinate."""
@@ -244,7 +238,6 @@ def test_add_scalar_depth_coord(cube_in, depth):
     assert coord == depth_coord
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube_in,height', TEST_ADD_SCALAR_COORD)
 def test_add_scalar_height_coord(cube_in, height):
     """Test adding of scalar height coordinate."""
@@ -272,7 +265,6 @@ def test_add_scalar_height_coord(cube_in, height):
     assert coord == height_coord
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube_in', TEST_ADD_SCALAR_COORD_NO_VALS)
 def test_add_scalar_lambda550nm_coord(cube_in):
     """Test adding of scalar lambda550nm coordinate."""
@@ -296,7 +288,6 @@ def test_add_scalar_lambda550nm_coord(cube_in):
     assert coord == lambda550nm_coord
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube_in,typeland', TEST_ADD_SCALAR_COORD)
 def test_add_scalar_typeland_coord(cube_in, typeland):
     """Test adding of scalar typeland coordinate."""
@@ -323,7 +314,6 @@ def test_add_scalar_typeland_coord(cube_in, typeland):
     assert coord == typeland_coord
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube_in,typesea', TEST_ADD_SCALAR_COORD)
 def test_add_scalar_typesea_coord(cube_in, typesea):
     """Test adding of scalar typesea coordinate."""
@@ -350,7 +340,6 @@ def test_add_scalar_typesea_coord(cube_in, typesea):
     assert coord == typesea_coord
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cube_in,typesi', TEST_ADD_SCALAR_COORD)
 def test_add_scalar_typesi_coord(cube_in, typesi):
     """Test adding of scalar typesi coordinate."""
@@ -377,7 +366,6 @@ def test_add_scalar_typesi_coord(cube_in, typesi):
     assert coord == typesi_coord
 
 
-@pytest.mark.sequential
 def test_cube_to_aux_coord():
     """Test converting cube to auxiliary coordinate."""
     cube = iris.cube.Cube(
@@ -405,7 +393,6 @@ def test_cube_to_aux_coord():
 ]
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('coord_name,output', TEST_GET_BOUNDS_CUBE)
 def test_get_bounds_cube(coord_name, output):
     """Test retrieving of bounds cube from list of cubes."""
@@ -443,7 +430,6 @@ def test_get_bounds_cube(coord_name, output):
 ]
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('var_names,output', TEST_FIX_BOUNDS)
 def test_fix_bounds(var_names, output):
     """Test retrieving of bounds cube from list of cubes."""
@@ -482,7 +468,6 @@ def test_fix_bounds(var_names, output):
 ]
 
 
-@pytest.mark.sequential
 @pytest.mark.parametrize('cubes_in,decimals,out', TEST_ROUND)
 def test_round_coordinate(cubes_in, decimals, out):
     """Test rounding of coordinates."""
@@ -497,7 +482,6 @@ def test_round_coordinate(cubes_in, decimals, out):
             assert coords[0] == out[idx]
 
 
-@pytest.mark.sequential
 def test_round_coordinates_single_coord():
     """Test rounding of specified coordinate."""
     coords, bounds = [10.0001], [[9.0001, 11.0001]]