My simple testing over the past few months (ie fill up with different brands and compare mileage from each) shows that Vortex is #1 with BP a smidge behind at #2.
Mobil (which I used to use religiously) is last by a mile (or should that be kilometre?)
The difference? Well consumption on Mobil has dropped to over 9 l/100 kms. BP I get around 8.5 l/100 kms and Caltex I get about 8.3 l/100 kms.
I used to get 8 l/100 kms from Mobil but i noticed it getting worse over time and so changed fuels to experiment.
I do around 115 km per weekday so I use about 1.5 tanks per week.
cheers
GAZ