In the U.S., all gasoline engined Mercedes since 1987 require 91 octane fuel. If you cannot obtain 91 octane fuel, you are told to use just enough lower octane fuel to get to a place where you can get premium. You are told not to exceed 2,000 RPM while using lower octane fuel. I just read this yesterday in a pamphlet from MB USA.

In the U.S., all BMW's, Mercedes, Lexus, Infinity's and Accuras require premium fuel. The lesser Japanese cars like Honda, Toyota, etc. take regular fuel.

Raising the compression ratio on an engine has the benefit of increasing both fuel economy and power at the cost of increased prices at the fuel pump.

I live in a very hot region of the U.S. and I've heard many American cars with pinging engines because they are told they can use 87 octane fuel. It's all about marketing. Those cars should be using at least 89 octane fuel but they are being marketed to people who are more worried about saving a few cents on fuel over long term reliability.

In the U.S., the cost of premium is about 10% higher than the cost of regular. Compared to the cost of depreciation or the money used to buy the car, the slight increased cost of premium fuel is insignificant.