Originally Posted by theholycow (Post 98054)

I thought it would be quick and easily to google for:
gasoline octane btu
and get the answer, but it's not. Anyway, I'm pretty sure that BTU content doesn't vary by octane rating, except as a result of the gasoline being diluted by whatever was used to raise the octane.

The reason higher octane rated gasoline can produce more power (or, in certain conditions, can produce more mileage) is because it can be used at a higher compression without pre-detonating. That allows the existing BTU content to be extracted more efficiently.

Edit: Simultaneous posts....dude, the gas you got was defective or contaminated, or coincidentally you've had a malfunction. Ask them if anyone else has been complaining about the 91 that they got that day.