Neither side created many chances during what was an unremarkable match at the Stadium of Light.
"I don't think we did enough to win the game," O'Neill told Sky Sports News. "We've had three games in a week but other teams have had the same.
"I just thought we looked a little jaded today - things looked like they were catching up with us.
"Wolves were always going to be difficult opponents; [they] always play with spirit. But we didn't do enough, that's the bottom line."
The Black Cats have moved up to ninth in the Premier League table following the draw.