Not that I'm complaining . . .

I find that my '01 lw300 seems to like some gas better than others. I usually average about 300 miles per tank (15 gallons capacity) on getty regular grade. I got some Amoco the other day and got almost 400 miles on the tank. Same driving patterns so I can only assume that the engine likes the Amoco additives better. Admittedly, this is not a scientific test. I don't keep records of how many gallons go into the tank so MPG is vague at best.

Bad O2 sensors will usually drag down your mileage. It's also possible that the different gas you used cleaned off a marginal sensor and improved the mileage. Oppie

Maybe Amoco pumps put more gas in a tank for a fill up.

Entirely possible... Also the flow rate from the pump. On the L series, there is a variable orifice on a float to the tank vent. It's supposed to cause the filling pump to shut off when the tank approaches full. You can get more fuel in the tank by filling slowly. I'm an engineer but not anal-retentive about keeping records on mpg . Being a bit mentally overloaded (overwhelmed) at work, I reserve all experimental protocols for the paying job.

Well hopefully you arent trying to estimate your fuel consumption via the fuel gage.