Striker James Constable was instrumental in Chris Wilder's side claiming their third league win in a row, scoring a superb 62nd minute goal and laying on the third for fellow substitute Asa Hall in the 78th.
After a goalless first half, striker Dean Smalley opened the scoring in the 48th minute, turning in David Hunt's corner at the near post.
Torquay's on-loan Derby striker Callum Ball responded by crashing a volley off the angle of the upright.
The Gulls had an effort ruled out - from Ball's free kick - before Constable latched on to a bouncing through ball to crash a text book dipping, right-footed volley past Gulls goalkeeper Martin Rice to make it 2-0.
Torquay substitute Jordan Chappell converted Karl Hawley's cross-cum-shot from the left at the far post and from close range with 20 minutes to go to half the deficit.
Oxford regained their two goal advantage when Hall latched on to Constable's pass to score at the second attempt after his first effort was saved by Rice.