My BMW tech in Ft. Lauderdale told me in 1990 to only run Amoco. It may just be superstition, but I have followed his advise religiously. After all, Amoco gas is interchangeable with Coleman lantern fuel, also refered to as 'White Gasoline'.

Two years ago the Amoco station by work was bought by a chain which sells Shell. I was lazy and continued to buy gas there. Within a month the check engine light came on and I had to replace the O2 sensor. (This was when I filled up every other day.)

It is also worth noting that when BP merged with Amoco, they stopped selling BP formulated gas in favor of Amoco.