What car should I buy?

[xoxoxoBruce]

Probably because Chevron was the first to qualify as "Top Tier Gasoline" in 2004, now there are about 30 in the US. They don't get better mileage, they have more detergent(s) to keep crap from building in the motor, which eventually will affect emissions, mileage and performance.

Tom Magliozzi, co-host of NPR's weekly radio show, Car Talk, said that using top tier detergent gasoline is only critical on high-end vehicles. For other vehicles, he and another source said that periodic use of a concentrated engine cleaner every 100,000 miles will "often" clean out carbon buildup.
Magliozzi's co-host, Ray Magliozzi, said that in order to be sure of preventing buildup of fuel injectors and valves, motorists should use Top Tier gasoline "at least most of the time".

[tw]

Originally Posted by xoxoxoBruce

They don't get better mileage, they have more detergent(s) to keep crap from building in the motor,

Mobil (decades before it became Exxon) had a highest detergent gas. It was not on the approved BMW list. Another study noted excessive detergents in Mobil resulted in carbon build up on valve stems.

Nothing previously discussed detergents. Additives mean more gas burns productively in the engine.

One night twenty some years ago, a Mobil station was the only open station. Next day, I knew something was wrong. Numbers confirmed it. Next tanks were a pathetic 27 and 25 MPG. I knew exactly when it happened - right after filling up at that Mobil station. The dealer identified damaged fuel injectors. I paid nothing to replace $400 of injectors. Mileage restored to above 30 MPG.