And, it equalled Blues' best away win since January 1998 when they beat Stoke City 7-0 at the Britannia Stadium.
The match began promisingly for Oxford with Joey Beauchamp bringing the best out of Blues keeper Kevin Poole after six minutes with a fierce shot from 20-yards out, but it all went wrong for the home side ten minutes later.
Martin Grainger hit a curling shot from 30 yards which Oxford's on-loan goal keeper Mike Salmon could only parry and the ball fell to the feet of Gary Rowett who was left with a simple tap-in.
Sixty seconds later Dele Adebola raced away from Phil Gilchrist and his low cross was swept in by Paul Furlong to make it two-nil.
There was no stopping the Blues now, they overwhelmed Oxford in midfield and from their first free-kick in the 31st minute Gary Ablett lifted the ball over the defence to Rowett who touched in his second goal of the match.
Two minutes before half time Adebola crossed from the left for Furlong to drive in for his second goal and Blues fourth.
Oxford keeper Salmon, signed on loan from Charlton, was having a nightmare and he was again beaten in the 55th minute. Grainger played a short corner to Steve Robinson and when the ball was returned to him he scored with a spectacular shot from 30 yards.
In the 72nd minute Poole set up the sixth with a massive clearance to Peter Ndlovu who ran through the Oxford defence unchallenged to score Blues sixth and a minute from time substitute Bryan Hughes slammed in Blues seventh.
Dean Windass headed a consolation for Oxford in the 90th minute.
Oxford Utd: Salmon, Robinson, Powell, Gray, Wilsterman, Gilchrist, Remy (Murphy 68), Smith, Thomson (Banger 68), Windass, Beauchamp. Subs Not Used: Rose.
Blues: Poole, Rowett, Grainger, Robinson, Ablett, Johnson, McCarthy (Marsh 69), Adebola (Hughes 69), Furlong, O'Connor, Ndlovu.
Referee: D Pugh (Wirral).