An oil change is a vital part of auto maintenance, but it’s not something most of us will do ourselves. So we’re also unlikely to know how to choose what kind of oil to put in the engine. Motor oil is integral to an engine’s performance—it keeps parts moving friction-free, prevents the engine’s temperature from getting too high, and cleans the engine as it circulates. But there are different types of oil that might be better options depending on how the engine operates.

Most mechanics or service centers will default to conventional motor oil, but read the following guide to know the difference between conventional and synthetic oil before you head to the shop:

Regular Oil

Regular, or conventional, motor oil is made from petroleum pumped from the ground. Oil refineries process this crude oil into various thicknesses, with thinner oils reserved for car engines and gas tanks. Unavoidably, natural impurities occur in regular motor oil, which is why owner’s manuals recommend an oil change every few thousand miles, as these impurities can build up in the form of “sludge.”

Synthetic Oil

As the name implies, synthetic oil is the result of manmade processes designed to produce the most efficient lubricant possible. In truth, most synthetics are born from natural oil and then purified at the molecular level. This means that all the molecules in synthetic oil are the same size, allowing it to maintain its viscosity better in extreme temperatures and help engines purr even in the darkest days of winter. Synthetic oil also lasts longer than its conventional counterpart and can prolong the life of an engine. However, it costs two to three times more than regular motor oil per oil change.