Peanut oil (arachis oil') is an organic material oil derived from peanuts, noted to have the slight aroma and taste of its parent legume. In the UK it is marketed as "groundnut oil".

It is often used in Chinese, South Asian and Southeast Asian cuisine much as olive oil is used in the Mediterranean. Peanut oil is appreciated for its high smoke point relative to many other cooking oils. Its major component fatty acids are oleic acid (56.6%) and linoleic acid (26.7%). The oil also contains some palmitic acid, arachidic acid, arachidonic acid, behenic acid, lignoceric acid and other fatty acids.

At the 1900 Paris Exhibition, the Otto Company, at the request of the French Government, demonstrated that peanut oil could be used as a source of fuel for the diesel engine.

It is also used as the main ingredient in some ear-wax removing products along with almond oil. Peanut oil is also used as a fecal softener.

Peanut oil is most commonly used when frying foods, particularly french fries and chicken.

Peanut oil is a monounsaturated fat. As such it may be substituted into a diet to reduce the negative health effects of eating trans fat and saturated fat.