diff --git a/tests/test_costs.py b/tests/test_costs.py
index ece4b29..d27fee1 100644
--- a/tests/test_costs.py
+++ b/tests/test_costs.py
@@ -44,6 +44,7 @@
         ("gpt-4-32k-0314", 15),
         ("gpt-4-1106-preview", 15),
         ("gpt-4-vision-preview", 15),
+        ("gpt-4o", 15),
     ],
 )
 def test_count_message_tokens(model, expected_output):
@@ -69,6 +70,7 @@ def test_count_message_tokens(model, expected_output):
         ("gpt-4-32k-0314", 17),
         ("gpt-4-1106-preview", 17),
         ("gpt-4-vision-preview", 17),
+        ("gpt-4o", 17),
     ],
 )
 def test_count_message_tokens_with_name(model, expected_output):
@@ -108,6 +110,7 @@ def test_count_message_tokens_invalid_model():
         ("gpt-4-1106-preview", 4),
         ("gpt-4-vision-preview", 4),
         ("text-embedding-ada-002", 4),
+        ("gpt-4o", 4)
     ],
 )
 def test_count_string_tokens(model, expected_output):
diff --git a/tokencost/costs.py b/tokencost/costs.py
index 0b098ef..feb931a 100644
--- a/tokencost/costs.py
+++ b/tokencost/costs.py
@@ -51,6 +51,10 @@ def count_message_tokens(messages: List[Dict[str, str]], model: str) -> int:
         "gpt-4-32k-0314",
         "gpt-4-0613",
         "gpt-4-32k-0613",
+        "gpt-4-turbo",
+        "gpt-4-turbo-2024-04-09",
+        "gpt-4o",
+        "gpt-4o-2024-05-13",
     }:
         tokens_per_message = 3
         tokens_per_name = 1
@@ -63,6 +67,10 @@ def count_message_tokens(messages: List[Dict[str, str]], model: str) -> int:
             "gpt-3.5-turbo may update over time. Returning num tokens assuming gpt-3.5-turbo-0613."
         )
         return count_message_tokens(messages, model="gpt-3.5-turbo-0613")
+    elif "gpt-4o" in model:
+        print(
+            "Warning: gpt-4o may update over time. Returning num tokens assuming gpt-4o-2024-05-13.")
+        return count_message_tokens(messages, model="gpt-4o-2024-05-13")
     elif "gpt-4" in model:
         logger.warning(
             "gpt-4 may update over time. Returning num tokens assuming gpt-4-0613."