They each add a proprietary additive package. Some are sophisticated and some are rather basic. I was never particularly sold on the value of these but some of the data can be impressive as far as cleaning deposits and keeping them off. The net result should be more power, more efficiency and more longevity with the better packages. The right gasoline can even make it easier for an automaker meet 100,000-mile emission testing standards.
I went to a media event at the Chevron Texaco campus last summer and met with their fuel engineers and North American V.P marketing celebrating their TOP TIER Gasoline rating (when they were about the first to earn it). This goes beyond EPA requirements and was developed by BMW, General Motors, Honda and Toyota as a “recommended” gasoline criteria for longevity and emissions, etc. I don’t go out of my way to buy branded gasoline, but I did get a bottle of Techron additive soon afterwards

FWIW, this is not a formal promotion of ChevronTexaco, but they do make an effort to be a leader in this category and they showed a real interesting before and after display using engine valves. According to their information a few tank fulls can clean away a lot of deposits. It seems the other majors are embracing “quality” gasoline again as well. Again, interesting but like many price tends to be king for me.
Charon