Thanks Winston,

I only gave that page a quick read at the top of the chart, I was on my way to work. That seems to confirm That there is not a significant difference in BTUÆs per gallon based on octane for pump gas that we can buy.

Not that we buy leaded but an example of how it can happen is adding lead in a small amount gives a large increase in octane but would not change the energy content noticeably. This same analogy would apply to BTUÆs per pound, take some 87 octane, add TEL till it hits 91, the density is not significantly changed but the octane is, therefore the BTUÆs per pound remains constant.

In other words, there are lots of ways to get high octane and depending on how you do it you can get more or less BTUÆs per gallon but there is not necessarily consistent correlation.

It seems the biggest factor is oxygenates to reduce smog / pollution. That explains my last experience on vacation. Once I got well out of California and got some real gas (non oxygenated) my fuel economy picked about 1.5 MPG up according to my cars MPG meter.

Seems to make sense to me.

Kevin C