After 5 tanks in my TCH, I found that my best tank average was when I used Arco ecUnleaded regular. I averaged 2mpg more than the other 4 tanks (37 vs 35) which used Shell unleaded regular. This might have been an abberation, but I drive the same route every day and have put 2000 miles on my car in the last 4 weeks.

Regarding gas in general, most of the "name brand" gasolines are the same high quality. A survey done many years ago showed that only Texaco showed a slightly better quality than the others, but not by much. I would think Costco, Safeway, and other national "non-petroleum" chains that sell large amounts of gas would be the same. But once you go to local mom&pop, the quality is not as good, and hence the price is cheaper. Why? The way gasoline is sold is that the most expensive gas is at the top of the container, because any sedatives/sludge sinks to the bottom. As the various merchants purchase their gas, the top of the container tank is more expensive, and the bottom of the tank is less expensive. Take a guess what part of the container "mom&pop gas station" gets their gas.