Vegetable oils will keep longer when refrigerated. Although some oils have a shelf life of a year or more, others such as flaxseed, sesame and walnut oils should be stored in the refrigerator. Eventually, all oils will become rancid with an off smell and taste. If this happens, it won't make you sick, but you should toss the oil anyway. To keep oil fresh longer, keep it away from heat, light and air.