1. It isn't the $/gallon that matters.... it is DOLLARS PER MILE that impacts the wallet. Duh.

A diesel will surpass a smaller gasser in terms of performance, an gets 10% better mileage and costs 10% more to fill. (26 versus 23 highway...worse around town) Thats a wash.

The larger motors may equal the diesel in driving performance (not stoplight racing) but cost more per mile- significantly (26 versus 20, way worse in the city.)

2. I fill the 996TT with 100 octane at 6/49 to 7.89 a gallon, depending on where I buy it.

I do not buy cars to save money. If I did there are a great many other cars - NOT BMW X5s- that will save me far more money than the price difference of the FUEL over the car's lifetime.....