Shell Optimax Vs BP Ultimate

[Dre911]

Some time back I posted on which is the best to use for 1998 996 C2. At the time it was considered to be optimax so that’s what I had been using I was getting about 200 miles on a full tank. Recently I was unable to fill up on Optimax and switched to BP ultimate, I noticed on the first tank my fuel consumption went up to 230 per tank, I've now tried this a few times and BP ultimate is consistently giving me more MPG than optimax...can someone help me telling me why when mostly others experience the opposite? PS Ultimate is more expensive than Optimax even though it's a lower RON rating ???

[verysideways]

optimax is a low sulphur fuel and so gets some sort of tax concession

i've always found optimax better on my 993's, but felt no difference between optimax and ultimate on my tvr chimaera.