The only detailed comparisons I have is from Targa last year - I was doing a job that required us to go through the stages before everyone and we were in a bit of a hurry (road was closed most of the time). I used BP98, Gull Force 10 and Mobil 8000, I found no discernable difference in fuel economy between any of them (we travelled in excess of 3000km during the week and used over $800 in fuel). However it was hardly the must subjective of tests, as we had different weather conditions, different levels of driver enthusiasm and different levels of weight onboard. So the only consistency was that it was the same car, driver and similar kays between refuels And yeah, no discernable economy difference.