[sliverstorm]

What do you drive? Typically the only cars that get really poor fuel economy with "Regular" are cars that specifically call for "Premium". When you fill them with "Regular", the computer essentially puts the engine in emergency limp-home-mode to prevent catastrophic damage, which reduces power and efficiency.

[tim-locke]

I drive a 1996 Honda Accord EX. It gets better mileage on Regular than Premium, but better mileage on Premium than E10 Regular, even after factoring in the price difference.