diff --git a/.github/workflows/core.yml b/.github/workflows/core.yml
index aae379b87..7883c5a7d 100644
--- a/.github/workflows/core.yml
+++ b/.github/workflows/core.yml
@@ -73,24 +73,50 @@ jobs:
         if: success() || steps.install.conclusion == 'success'
         run: |
           . venv-thetis/bin/activate
-          : # Run the serial tests
+          : # Run the serial tests, excluding examples which are tested separately
           python -m pytest -n 12 --verbose --durations=0 --durations-min=60.0 \
-            -m "parallel[1] or not parallel" thetis-repo/test
+            --ignore=thetis-repo/test/examples \
+            -m parallel[match] thetis-repo/test
 
       - name: Test Thetis (parallel)
         if: success() || steps.install.conclusion == 'success'
         run: |
           . venv-thetis/bin/activate
-          : # Run the parallel tests (note that xdist is not valid in parallel)
-          mpiexec -n 2 python -m pytest --verbose --durations=0 --durations-min=60.0 \
-            -m parallel[2] thetis-repo/test
+          : # Split the parallel tests into multiple mpiexec jobs to utilise all cores
+          export FIREDRAKE_RUN_SPLIT_TESTS_TIMEOUT=660s
+          export FIREDRAKE_RUN_SPLIT_TESTS_KILL_AFTER=30s
+          firedrake-run-split-tests 2 4 \
+            --durations=0 --durations-min=60.0 \
+            --timeout=600 --timeout-method=thread \
+            thetis-repo/test
 
-      - name: Test Thetis adjoint
+      - name: Test Thetis examples (serial)
         if: success() || steps.install.conclusion == 'success'
         run: |
-          firedrake-clean
           . venv-thetis/bin/activate
-          python -m pytest -n 8 --verbose --durations=0 thetis-repo/test_adjoint
+          python -m pytest -n 12 --verbose --durations=0 --durations-min=60.0 \
+            -m parallel[match] \
+            thetis-repo/test/examples thetis-repo/test_adjoint/examples
+
+      - name: Test Thetis adjoint (serial)
+        if: success() || steps.install.conclusion == 'success'
+        run: |
+          . venv-thetis/bin/activate
+          python -m pytest -n 2 --verbose --durations=0 --durations-min=60.0 \
+            --ignore=thetis-repo/test_adjoint/examples \
+            -m parallel[match] thetis-repo/test_adjoint
+
+      - name: Test Thetis adjoint (parallel)
+        if: success() || steps.install.conclusion == 'success'
+        run: |
+          . venv-thetis/bin/activate
+          : # Split the parallel tests into multiple mpiexec jobs to utilise all cores
+          export FIREDRAKE_RUN_SPLIT_TESTS_TIMEOUT=660s
+          export FIREDRAKE_RUN_SPLIT_TESTS_KILL_AFTER=30s
+          firedrake-run-split-tests 2 1 \
+            --durations=0 --durations-min=60.0 \
+            --timeout=600 --timeout-method=thread \
+            thetis-repo/test_adjoint
 
       - name: Post-cleanup
         if: always()
diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index fa4fbcedb..cdf400aa7 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -9,5 +9,5 @@ jobs:
     uses: ./.github/workflows/core.yml
     with:
       branch: ${{ github.event.pull_request.head.sha }}
-      image: ${{ github.base_ref == 'release' && 'firedrakeproject/firedrake-vanilla-default:latest' || 'firedrakeproject/firedrake-vanilla-default:dev-main' }}
+      image: ${{ github.base_ref == 'release' && 'firedrakeproject/firedrake-vanilla-default:dev-release' || 'firedrakeproject/firedrake-vanilla-default:dev-main' }}
     secrets: inherit
diff --git a/.github/workflows/push.yml b/.github/workflows/push.yml
index 7364ce8bc..dfe19045b 100644
--- a/.github/workflows/push.yml
+++ b/.github/workflows/push.yml
@@ -11,5 +11,5 @@ jobs:
     uses: ./.github/workflows/core.yml
     with:
       branch: ${{ github.ref_name }}
-      image: ${{ github.ref_name == 'release' && 'firedrakeproject/firedrake-vanilla-default:latest' || 'firedrakeproject/firedrake-vanilla-default:dev-main' }}
+      image: ${{ github.ref_name == 'release' && 'firedrakeproject/firedrake-vanilla-default:dev-release' || 'firedrakeproject/firedrake-vanilla-default:dev-main' }}
     secrets: inherit
diff --git a/.github/workflows/weekly-release.yml b/.github/workflows/weekly-release.yml
index b9f1d959d..711acfae1 100644
--- a/.github/workflows/weekly-release.yml
+++ b/.github/workflows/weekly-release.yml
@@ -12,5 +12,5 @@ jobs:
     uses: thetisproject/thetis/.github/workflows/core.yml@release
     with:
       branch: release
-      image: firedrakeproject/firedrake-vanilla-default:latest
+      image: firedrakeproject/firedrake-vanilla-default:dev-release
     secrets: inherit
diff --git a/.gitignore b/.gitignore
index b063d17b8..5b587d8c3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -42,6 +42,7 @@ htmlcov/
 nosetests.xml
 coverage.xml
 *,cover
+*.errcode
 
 # Translations
 *.mo
diff --git a/examples/tohoku_inversion/inverse_problem.py b/examples/tohoku_inversion/inverse_problem.py
index 4115f22fa..5e63885db 100644
--- a/examples/tohoku_inversion/inverse_problem.py
+++ b/examples/tohoku_inversion/inverse_problem.py
@@ -48,6 +48,9 @@
 source = get_source(mesh2d, source_model)
 if source_model == "okada":
     source.subfault_variables = args.okada_parameters
+    if os.getenv('THETIS_REGRESSION_TEST') is not None:
+        source.num_subfaults_par = 2
+        source.num_subfaults_perp = 2
 
 # Setup PDE
 output_dir = f"{pwd}/outputs_elev-init-optimization_{source_model}"
diff --git a/test/examples/test_examples.py b/test/examples/test_examples.py
index d73a8a5ef..c3743a4a1 100644
--- a/test/examples/test_examples.py
+++ b/test/examples/test_examples.py
@@ -7,6 +7,7 @@
 import glob
 import sys
 import shutil
+import runpy
 
 # set environment flag
 # can be used in examples to reduce cpu cost
@@ -68,18 +69,65 @@
 all_examples = glob.glob(os.path.join(examples_dir, '*/*.py'))
 all_examples = [f for f in all_examples if f not in exclude_files]
 
+# Examples that should be exercised under MPI in the main parallel CI job.
+# Keyed by path relative to `examples_dir` with the requested nprocs.
+parallel_examples = {
+    os.path.join('discrete_turbines', 'tidal_array.py'): 2,
+}
 
-@pytest.fixture(params=all_examples)
+for relpath, nprocs in parallel_examples.items():
+    abspath = os.path.join(examples_dir, relpath)
+    try:
+        idx = all_examples.index(abspath)
+    except ValueError:
+        continue
+    all_examples[idx] = pytest.param(abspath, marks=pytest.mark.parallel(nprocs))
+
+
+@pytest.fixture(params=all_examples,
+                ids=lambda x: os.path.relpath(x, examples_dir))
 def example_file(request):
     return os.path.abspath(request.param)
 
 
-def test_examples(example_file, tmpdir, monkeypatch):
+def test_examples(example_file, tmp_path, monkeypatch, request):
     assert os.path.isfile(example_file), 'File not found {:}'.format(example_file)
     # copy mesh files
     source = os.path.dirname(example_file)
-    for f in glob.glob(os.path.join(source, '*.msh')):
-        shutil.copy(f, str(tmpdir))
-    # change workdir to temporary dir
-    monkeypatch.chdir(tmpdir)
-    subprocess.check_call([sys.executable, example_file])
+
+    if request.node.get_closest_marker("parallel") is None:
+        # Serial example: copy mesh files and run in a subprocess.
+        for f in glob.glob(os.path.join(source, '*.msh')):
+            shutil.copy(f, str(tmp_path))
+        # change workdir to temporary dir
+        monkeypatch.chdir(tmp_path)
+        subprocess.check_call([sys.executable, example_file])
+        return
+
+    # Parallel example: run the script under the current MPI communicator.
+    # In CI this test is selected only in the main parallel job (outer mpiexec -n 2),
+    # so we must not spawn mpiexec here (no nested MPI). We also coordinate a shared
+    # working directory across ranks to avoid each rank creating its own tmp_path.
+    from mpi4py import MPI
+    comm = MPI.COMM_WORLD
+    if comm.rank == 0:
+        workdir = tmp_path
+        for f in glob.glob(os.path.join(source, '*.msh')):
+            shutil.copy(f, str(workdir))
+    else:
+        workdir = None
+    workdir = comm.bcast(str(workdir) if workdir is not None else None, root=0)
+    comm.barrier()
+    monkeypatch.chdir(workdir)
+    # Make local imports like `import turbine_callback` work the same way they do
+    # when running `python /abs/path/to/example.py` (which prepends the script dir
+    # to sys.path).
+    added_to_syspath = False
+    if source not in sys.path:
+        sys.path.insert(0, source)
+        added_to_syspath = True
+    try:
+        runpy.run_path(example_file, run_name="__main__")
+    finally:
+        if added_to_syspath and sys.path and sys.path[0] == source:
+            sys.path.pop(0)
diff --git a/test_adjoint/conftest.py b/test_adjoint/conftest.py
index 3e4f20137..4f437b434 100644
--- a/test_adjoint/conftest.py
+++ b/test_adjoint/conftest.py
@@ -5,4 +5,7 @@ def pytest_runtest_teardown(item, nextitem):
     from pyadjoint import get_working_tape
 
     # clear the adjoint tape, so subsequent tests don't interfere
-    get_working_tape().clear_tape()
+    tape = get_working_tape()
+    # Some tests run external scripts and never create a tape in the main pytest process.
+    if tape is not None:
+        tape.clear_tape()
diff --git a/test_adjoint/examples/test_adjoint_examples.py b/test_adjoint/examples/test_adjoint_examples.py
new file mode 100644
index 000000000..ebf3502fd
--- /dev/null
+++ b/test_adjoint/examples/test_adjoint_examples.py
@@ -0,0 +1,75 @@
+"""
+Runs all adjoint example scripts. Only tests whether examples can be executed.
+"""
+import pytest
+import os
+import subprocess
+import glob
+import sys
+import shutil
+import runpy
+
+# set environment flag
+# can be used in examples to reduce cpu cost
+os.environ['THETIS_REGRESSION_TEST'] = "1"
+
+# list of all adjoint examples to run
+adjoint_files_serial = [
+    'tidalfarm/tidalfarm.py',
+    'channel_inversion/inverse_problem.py',
+    'headland_inversion/inverse_problem.py',
+    'tohoku_inversion/inverse_problem.py',
+]
+
+adjoint_files_parallel = [
+    'discrete_turbines/channel-optimisation.py',
+]
+
+cwd = os.path.abspath(os.path.dirname(__file__))
+examples_dir = os.path.abspath(os.path.join(cwd, '..', '..', 'examples'))
+
+all_examples = (
+    [os.path.join(examples_dir, f) for f in adjoint_files_serial]
+    + [
+        pytest.param(os.path.join(examples_dir, f), marks=pytest.mark.parallel(2))
+        for f in adjoint_files_parallel
+    ]
+)
+
+
+@pytest.fixture(params=all_examples,
+                ids=lambda x: os.path.relpath(x, examples_dir))
+def example_file(request):
+    return os.path.abspath(request.param)
+
+
+def test_examples(example_file, tmp_path, tmp_path_factory, monkeypatch, request):
+    assert os.path.isfile(example_file), 'File not found {:}'.format(example_file)
+    # copy mesh files
+    source = os.path.dirname(example_file)
+
+    if request.node.get_closest_marker("parallel") is None:
+        # Serial example: copy mesh files and run in a subprocess.
+        for f in glob.glob(os.path.join(source, '*.msh')):
+            shutil.copy(f, str(tmp_path))
+        # change workdir to temporary dir
+        monkeypatch.chdir(tmp_path)
+        subprocess.check_call([sys.executable, example_file])
+        return
+
+    # Parallel example: run the script under the current MPI communicator.
+    # In CI this test is selected only in the adjoint-parallel job (outer mpiexec -n 2),
+    # so we must not spawn mpiexec here (no nested MPI). We also coordinate a shared
+    # working directory across ranks to avoid each rank creating its own tmpdir.
+    from mpi4py import MPI
+    comm = MPI.COMM_WORLD
+    if comm.rank == 0:
+        workdir = tmp_path_factory.mktemp("thetis-adjoint-example-channel-optimisation")
+        for f in glob.glob(os.path.join(source, '*.msh')):
+            shutil.copy(f, str(workdir))
+    else:
+        workdir = None
+    workdir = comm.bcast(str(workdir) if workdir is not None else None, root=0)
+    comm.barrier()
+    monkeypatch.chdir(workdir)
+    runpy.run_path(example_file, run_name="__main__")
diff --git a/test_adjoint/examples/test_examples.py b/test_adjoint/examples/test_examples.py
deleted file mode 100644
index bfba102ac..000000000
--- a/test_adjoint/examples/test_examples.py
+++ /dev/null
@@ -1,46 +0,0 @@
-"""
-Runs all adjoint example scripts. Only tests whether examples can be executed.
-"""
-import pytest
-import os
-import subprocess
-import glob
-import sys
-import shutil
-
-# set environment flag
-# can be used in examples to reduce cpu cost
-os.environ['THETIS_REGRESSION_TEST'] = "1"
-
-# list of all adjoint examples to run
-adjoint_files = [
-    'tidalfarm/tidalfarm.py',
-    'channel_inversion/inverse_problem.py',
-    'headland_inversion/inverse_problem.py',
-    'tohoku_inversion/inverse_problem.py',
-    'discrete_turbines/channel-optimisation.py',
-]
-
-cwd = os.path.abspath(os.path.dirname(__file__))
-examples_dir = os.path.abspath(os.path.join(cwd, '..', '..', 'examples'))
-
-include_files = [os.path.join(examples_dir, f) for f in adjoint_files]
-
-all_examples = include_files
-
-
-@pytest.fixture(params=all_examples,
-                ids=lambda x: os.path.basename(x))
-def example_file(request):
-    return os.path.abspath(request.param)
-
-
-def test_examples(example_file, tmpdir, monkeypatch):
-    assert os.path.isfile(example_file), 'File not found {:}'.format(example_file)
-    # copy mesh files
-    source = os.path.dirname(example_file)
-    for f in glob.glob(os.path.join(source, '*.msh')):
-        shutil.copy(f, str(tmpdir))
-    # change workdir to temporary dir
-    monkeypatch.chdir(tmpdir)
-    subprocess.check_call([sys.executable, example_file])