Do You Need to Pay for Premium Gas?

Most modern engines are made to operate on regular, which is the least expensive and most common fuel in most states. Regardless of octane rating, most gas sold in the U.S. is 10 percent ethanol, an additive made from crops like corn and sugarcane. You may also see E15 or 88 (15 percent ethanol) which can be used in most cars made since 2001, and E85 (85 percent ethanol), which can be used only in “flex-fuel” vehicles. Check your owner’s manual to be sure.

Expert tip: Although E15 and E85 may cost less, ethanol also contains less energy than gasoline. That means higher-ethanol blends will result in lower fuel economy.

This fuel may benefit only a handful of vehicles. Otherwise, save your money. “Some drivers think that putting 89 in a car that only requires 87 is better for the engine,” Fisher says. “But that’s not true.” If you want fuel that’s truly better for your engine, look for the Top Tier label. Top Tier gasolines contain detergents that help prevent carbon buildup, which can hurt performance and reduce fuel economy over time, according to a study from AAA.

Expert tip: Whatever your octane, buy Top Tier gas. Most major gas stations—BP, Costco, Chevron, ExxonMobil, Shell— offer it. Check CR.org/toptiergas for a full list.

“There’s a big difference between the words ‘recommended’ and ‘required,’” Fisher says. If your vehicle owner’s manual or fuel flap says that premium is recommended, it’s safe to use 87 for daily driving. However, if your car says premium is required, the manufacturer specifically designed the engine to run on higher-octane fuel. This is more common in luxury or performance cars. In these cases, not using premium could damage the engine or void your warranty.

Expert tip: If you plan to stress a premium-recommended car by towing, or driving in the mountains or in extremely hot weather, fill up with premium. It will reduce the risk of engine knock.