* If "oh" is used as an interjection expressing surprise or realization, it typically does NOT need a comma.
* Example: "Oh, I didn't realize you were here."
* If "oh" is used as a part of a phrase, it might need a comma depending on the surrounding sentence structure.
* Example: "Oh, how I wish I could go." (comma after "oh" because it introduces a dependent clause)
Here are some examples to help you understand:
* No comma: Oh, I didn't see you there.
* No comma: Oh how beautiful!
* Comma: Oh, the weather is perfect today.
* Comma: Oh, I see what you mean now.
In general, it's safe to assume that "oh" as an interjection does not require a comma, but if you're unsure, it's always best to consult a grammar guide or style manual.