Charlton held Oxford to a 1-1 draw at the Kassam Stadium to deny the U's a fourth successive league win.
In a high-quality clash between teams in the play-off positions, Oxford did most of the pressing, but they had to come from behind to claim a point.
Tarique Fosu put the Addicks ahead in the 18th minute when he charged down Curtis Nelson's clearance and touched the ball past keeper Simon Eastwood before running on to score.
But the U's equalised 10 minutes before half-time when right back Christian Ribeiro bagged his first goal for the club. James Henry's right-wing cross was poorly headed out by Chris Solly and Ribeiro fired a left-foot volley into the net.
Oxford finished the half strongly with Josh Ruffels curling a shot wide, and Ricardinho's drive blocked on the line by Jake Forster-Caskey.
In the second half, Wes Thomas was twice denied by Ben Amos, but Charlton also went close with Fosu scooping a shot wide, and Eastwood saving from Billy Clarke.