One of the simplest substitutes for oil in a cake recipe is an equal amount of melted unsalted butter. If all you have is salted butter on hand, simply adjust the amount of salt called for in the recipe when baking a cake from scratch. It's best to stick with unsalted butter if you're using a packaged cake mix, unless you don't mind a slightly saltier taste in your cake. When using melted butter, be sure it's completely melted and cooled enough to add to the batter.

Fruit purees have relatively the same thick liquid texture as vegetable oil and melted butter, but contain much less fat. Choices include unsweetened canned or homemade smooth applesauce or a puree made from any type of fruit, including prunes, apricots, peaches or bananas. Try to match the flavor intensity of the puree to that of your cake, as the stronger taste of prunes or bananas may alter the flavor of a mild-flavored batter such as yellow cake. Substitute the same amount of fruit sauce or puree as the amount of oil called for in the recipe and add it with the other wet ingredients.

The word mayonnaise usually conjures up images of ham sandwiches or potato salad, but it can also replace the oil in a cake made from scratch or one made from a packaged cake mix. Aside from the acid used to make mayonnaise, which is usually vinegar, it's made primarily by blending oil with eggs. It has the same creamy texture and binding capabilities as oil, and can be used as a substitute for the oil without altering the flavor of a cake. Simply swap the same amount of mayo for the amount of oil called for in your recipe or in the cake mix directions.

melted margarine can also be a suitable substitute for the oil called for in a cake recipe as long as it is made of 80 percent fat and 20 percent water, which is the same as butter. Developed in Europe during the 1800s as a healthier alternative to butter, today's margarines are often further watered down to lower their fat content even more. Available in sticks or spreads, they generally cannot be substituted for vegetable oil unless a recipe specifically calls for it, as their higher water content can affect a cake's texture and flavor.