diff --git a/langextract/providers/patterns.py b/langextract/providers/patterns.py
index 9fd18cab..27f2632a 100644
--- a/langextract/providers/patterns.py
+++ b/langextract/providers/patterns.py
@@ -24,10 +24,12 @@
 
 # OpenAI provider patterns
 OPENAI_PATTERNS = (
+    r'^gpt-3\.5',  # gpt-3.5-turbo, gpt-3.5-turbo-16k, etc.
     r'^gpt-4',
     r'^gpt4\.',
     r'^gpt-5',
     r'^gpt5\.',
+    r'^o[1-9]',  # reasoning models: o1, o3, o3-mini, o4-mini, etc.
 )
 OPENAI_PRIORITY = 10
 
diff --git a/tests/registry_test.py b/tests/registry_test.py
index fa907067..b5822923 100644
--- a/tests/registry_test.py
+++ b/tests/registry_test.py
@@ -149,6 +149,20 @@ def test_load_builtins_once_deduplicates_and_recovers_after_clear(self):
 
     self.assertEqual(router.list_providers(), first_providers)
 
+  def test_openai_patterns_cover_reasoning_and_gpt35_models(self):
+    """OpenAI o-series and gpt-3.5 model IDs resolve to the OpenAI provider."""
+    providers_module._builtins_loaded = False  # pylint: disable=protected-access
+    providers_module.load_builtins_once()
+
+    for model_id in ("o1", "o3-mini", "o4-mini", "gpt-3.5-turbo", "gpt-4o"):
+      with self.subTest(model_id=model_id):
+        resolved = router.resolve(model_id)
+        self.assertEqual(resolved.__name__, "OpenAILanguageModel")
+
+    # The o-series pattern must not swallow other o-prefixed model IDs.
+    with self.assertRaises(exceptions.InferenceConfigError):
+      router.resolve("openchat")
+
   def test_list_entries(self):
     """Test listing registered entries."""
     router.register_lazy(r"^test1", target="fake:Target1", priority=5)