For oils that you may use infrequently or over a long period of time, such as sesame, walnut, chili, peanut and the like, or big jugs of anything, you can prevent them from becoming rancid after you open them by adding the contents of a capsule of vitamin E, an antioxident, to the bottle and mixing. I though this was New Age hooey when I first read it but it really works. My Mom, not a gifted cook, always cooked in Wesson oil, and for years I avoided it like the plague because of hugley unpleasant childhood memories. It wasn't until years later that I realized that it wasn't that Wesson oil sucked, but the nasty taste and smell were because the oil had turned rancid. Try it!