Coventry have now failed to win any of their last three games
Coventry City's winless run extended to three matches as the Championship leaders were held to a scoreless draw.
U's striker Will Lankshear - who is on loan from Premier League side Tottenham - was shown a second yellow card and sent off with 13 minutes remaining.
But Coventry could not take advantage and second-placed Middlesborough will now move top of the table on Monday if they win away to Sheffield United.
Matt Bloomfield's Oxford remain 23rd in the Championship table and four points from safety.
The hosts dominated the ball in the first half, having nine shots, with three of those on target.
Early on, Matt Grimes made a burst through midfield and let fly with a dangerous right-footed shot which flew narrowly past the right-hand post.
Tatsuhiro Sakamoto then had a great chance to open the scoring just after the half-hour mark, shooting low towards the bottom right-hand corner but U's keeper Jamie Cumming made a brilliant save.
Oxford's best chance of the half came when Christ Makosso's super pass found Przemysław Płacheta, but the winger's attempt on goal went behind for a goal-kick.
Oxford's Cumming was thanked again by his team-mates just after the hour mark when he denied Romain Esse with a great save after the Coventry man curled a shot towards the bottom corner from outside the box.
The U's were then reduced to 10 men as substitute Will Lankshear was shown his second yellow card having come on just 20 minutes earlier
The striker barged into Coventry's Joel Latibeaudiere in an attempt to break in behind and the referee gave him his marching orders.
Frank Lampard's side pushed late on to break the deadlock, but the Oxford backline held firm and the points were shared.
'We were very good up to the last bit' - reaction
Coventry City boss Frank Lampard told BBC Radio Coventry and Warwickshire:
"It's a frustrating result but the lads did everything.
"There's lots of positives in the performance though, we dominated every part of it really and didn't give anything away other than maybe one counter-attack in the first half. Other than that it was all us, the ball wasn't going in the net though.
"We were very good up to the last bit - it's not easy against a dogged team that set up in a low block.
"We tried a lot and we created enough to win the game, but it didn't happen for us."
Oxford United boss Matt Bloomfield told BBC Radio Oxford:
"Thank you to the fans for their support today through the game and at the end. They certainly recognise the grit and determination the players played with today.
"It was always going to be a tough game coming away to the team top of the table, but the way the boys dug in and showed resilience I'm incredibly proud of them today.
"Going away from home to the leaders and getting a point is a really good point - we have to be incredibly proud, getting a clean sheet, too."
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