[ivymike1031]

yep...

I think it's important to keep in mind that the octane number on your fuel from the gas station doesn't really tell you anything about the composition of the fuel, except that whatever is in there has anti-knock properties similar to a particular mixture of octane/heptane. In other words, 87 octane gas from the station isn't likely to be 87% octane, 13% heptane, it just knocks as though it was.