You do not need to have oil to prepare a packaged cake mix. Melted butter or applesauce can stand in for oil in any cake mix. You will still need the other ingredients required for the mix on the side of the box. Using applesauce will reduce the fat and overall calories, and using melted butter will add a light buttery flavor. Opt for the oil replacement that best suits your tastes and diet.
Replace the oil in your recipe with the same amount of cooled melted butter or applesauce.
Add the replacement to the cake mix when the instructions indicate the oil is added.
Bake the cake for the same time and temperature as listed on the side of the box.