If unopened and kept in a cool, dark place (like a pantry or basement) refined peanut oil has a long shelf life and can last up to a year or more. Once opened and exposed to heat and light, however, it will eventually go rancid, usually within 4 to 6 months (rancid peanut oil will have a rancid odor). You can extend the shelf life of peanut oil by keeping it in the refrigerator.