You may get better results by breaking up your aerobic exercise into shorter periods seperated by a rest period. It appears the fat metabolism is enhanced during the second session.
In the study, they compared a 60 minute aerobic session with 2 30 minute sessions with a 20 minute rest in between. All paramaters indicated enhanced fat burning during the second session far greater than in the continuous session.
Of course, this would all be thrown out the window if you take in any food during the rest period.