A friend of mine said that he could apparently get better mileage using Chevron oil instead of Shell's (and other brands). Is there any substance to this claim?
According to The Gasoline Wars Chemical & Engineering News, vol. 87, pages 20-21, there are differences in the detergent content of gasolines. The 2009 article stated:
detergent levels dropped far enough earlier this decade that in 2004, automakers BMW, General Motors, Honda, and Toyota got together to create a standard for gasoline detergents called Top Tier. Marketers seeking to qualify their fuels as Top Tier Detergent Gasoline must pass tests for intake valve cleanliness, fuel injector fouling, and the like. Chevron and Shell are on the list, but other big brands like BP and Exxon are not.
The article explains that different brands vary in terms of the amount and chemical nature of the detergent additives.
According to The analytical report on Consumer Gasoline Choices, conducted by Michael Stanley of Cleveland State University in 2015:
The major differences found in gasoline are the octane grade and the additives packages that gasoline retailers include in their fuel to create specific brands. Choosing the best gasoline for a vehicle first involves consulting the dealer or owner’s manual to determine w hat octane rating is appropriate for the vehicle. The second part of choosing the best gasoline involves using a brand of gas with higher levels of beneficial additives and detergents.
Choosing the right gasoline for a particular vehicle is one of the few options drivers have that can significantly improve or hinder the overall performance of their vehicle, as well as one of the most important choices for preventative maintenance. Continued use of low detergent fuel can cause lower fuel economy, loss of power, and fuel deposit buildup in engine parts with the potential for damage to the internal engine parts.
Consumers that want the best fuel should know the octane rating of their vehicle and always use that grade of fuel. To prevent harmful fuel deposit buildup, increase gas mileage, and boost engine power, consumers should use gas from a Top Tier gasoline retailer regularly to be sure the fuel they put in their gas tank meets minimum additive and detergent levels recommended by several automobile manufactures, and to maximize the benefits of clean burni ng efficient fuel.