diff --git a/petsctools/__init__.py b/petsctools/__init__.py
index 58293cc..878b76b 100644
--- a/petsctools/__init__.py
+++ b/petsctools/__init__.py
@@ -14,7 +14,11 @@
 # is not available then attempting to access these attributes will raise an
 # informative error.
 if PETSC4PY_INSTALLED:
-    from .citation import add_citation, cite, print_citations_at_exit  # noqa: F401
+    from .citation import (  # noqa: F401
+        add_citation,
+        cite,
+        print_citations_at_exit,
+    )
     from .config import get_blas_library  # noqa: F401
     from .init import (  # noqa: F401
         InvalidEnvironmentException,
diff --git a/petsctools/options.py b/petsctools/options.py
index 5e5ef58..dc78f4a 100644
--- a/petsctools/options.py
+++ b/petsctools/options.py
@@ -1,10 +1,11 @@
 from __future__ import annotations
 
+import weakref
 import contextlib
 import functools
 import itertools
 import warnings
-from typing import Any
+from typing import Any, Iterable
 
 import petsc4py
 
@@ -90,12 +91,42 @@ def munge(keys):
         if option in new:
             warnings.warn(
                 f"Ignoring duplicate option: {option} (existing value "
-                f"{new[option]}, new value {value})",
+                f"{new[option]}, new value {value})", PetscToolsWarning
             )
         new[option] = value
     return new
 
 
+def _warn_unused_options(all_options: Iterable, used_options: Iterable,
+                         options_prefix: str = ""):
+    """
+    Raise warnings for PETSc options which were not used.
+
+    This is meant only as a weakref.finalize callback for the OptionsManager.
+
+    Parameters
+    ----------
+    all_options :
+        The full set of options passed to the OptionsManager.
+    used_options :
+        The options which were used during the OptionsManager's lifetime.
+    options_prefix :
+        The options_prefix of the OptionsManager.
+
+    Raises
+    ------
+        PetscToolsWarning :
+            For every entry in all_options which is not in used_options.
+    """
+    unused_options = set(all_options) - set(used_options)
+
+    for option in sorted(unused_options):
+        warnings.warn(
+            f"Unused PETSc option: {options_prefix+option}",
+            PetscToolsWarning
+        )
+
+
 class OptionsManager:
     """Class that helps with managing setting PETSc options.
 
@@ -238,8 +269,17 @@ def __init__(self, parameters: dict, options_prefix: str | None):
             # since that does not DTRT for flag options.
             for k, v in self.options_object.getAll().items():
                 if k.startswith(self.options_prefix):
-                    self.parameters[k[len(self.options_prefix) :]] = v
+                    self.parameters[k[len(self.options_prefix):]] = v
         self._setfromoptions = False
+        # Keep track of options used between invocations of inserted_options().
+        self._used_options = set()
+
+        # Decide whether to warn for unused options
+        with self.inserted_options():
+            if self.options_object.getInt("options_left", 0) > 0:
+                weakref.finalize(self, _warn_unused_options,
+                                 self.to_delete, self._used_options,
+                                 options_prefix=self.options_prefix)
 
     def set_default_parameter(self, key: str, val: Any) -> None:
         """Set a default parameter value.
@@ -292,6 +332,8 @@ def inserted_options(self):
             yield
         finally:
             for k in self.to_delete:
+                if self.options_object.used(self.options_prefix + k):
+                    self._used_options.add(k)
                 del self.options_object[self.options_prefix + k]
 
     @functools.cached_property
diff --git a/tests/test_options.py b/tests/test_options.py
new file mode 100644
index 0000000..c6bd759
--- /dev/null
+++ b/tests/test_options.py
@@ -0,0 +1,76 @@
+import warnings
+import pytest
+import petsctools
+
+
+@pytest.fixture(autouse=True, scope="module")
+def temporarily_remove_options():
+    """Remove all options when the module is entered and reinsert them at exit.
+    This ensures that options in e.g. petscrc files will not pollute the tests.
+    """
+    if petsctools.PETSC4PY_INSTALLED:
+        PETSc = petsctools.init()
+        options = PETSc.Options()
+        previous_options = {
+            k: v for k, v in options.getAll().items()
+        }
+        options.clear()
+    yield
+    if petsctools.PETSC4PY_INSTALLED:
+        for k, v in previous_options.items():
+            options[k] = v
+
+
+@pytest.fixture(autouse=True)
+def clear_options():
+    """Clear any options from the database at the end of each test.
+    """
+    yield
+    # PETSc already initialised by module scope fixture
+    from petsc4py import PETSc
+    PETSc.Options().clear()
+
+
+@pytest.mark.skipnopetsc4py
+@pytest.mark.parametrize("options_left", (-1, 0, 1),
+                         ids=("no_options_left",
+                              "options_left=0",
+                              "options_left=1"))
+def test_unused_options(options_left):
+    """Check that unused solver options result in a warning in the log."""
+    # PETSc already initialised by module scope fixture
+    from petsc4py import PETSc
+
+    if options_left >= 0:
+        PETSc.Options()["options_left"] = options_left
+
+    parameters = {
+        "used": 1,
+        "not_used": 2,
+    }
+    options = petsctools.OptionsManager(parameters, options_prefix="optobj")
+
+    with options.inserted_options():
+        _ = PETSc.Options().getInt(options.options_prefix + "used")
+
+    # No warnings should be raised in this case.
+    if options_left <= 0:
+        with warnings.catch_warnings():
+            warnings.simplefilter("error")
+            del options
+        return
+
+    # Destroying the object will trigger the unused options warning
+    with pytest.warns() as records:
+        del options
+
+    # Exactly one option is both unused and not ignored
+    assert len(records) == 1
+    message = str(records[0].message)
+
+    # Does the warning include the options prefix?
+    assert "optobj" in message
+
+    # Do we only raise a warning for the unused option?
+    assert "optobj_not_used" in message
+    assert "optobj_used" not in message