Oxford gained their second league win of the season when they condemned Hereford to their fourth consecutive defeat in League Two.
Oxford were the more positive side in the early stages with Tom Craddock heading a cross from James Constable straight at goalkeeper Adam Bartlett.
Bartlett also saved a powerful 25-yard drive from Asa Hall as Oxford piled on the pressure and he made three more saves to deny Constable before the striker put Oxford in front in the 35th minute.
Matt Green broke clear on the right before releasing the ball to Constable, who beat Bartlett from close range at the second attempt.
After the break Craddock went close to increasing Oxford's lead when he turned the ball past the Hereford post from a corner by Ben Purkiss.
Craddock however clinched Oxford's victory in the 65th minute when he lashed a 15-yard shot into the roof of the Hereford net.