In substituting one ingredient for another, it is important to note how the new ingredient will change the taste and texture of a recipe. Method of cooking is also a factor in determining what ingredients may stand in for others.
Cooking
In cooking, shortening can be substituted for vegetable oil in a 1-to-1 ratio. Shortening is better as a substitute for vegetable oil than butter for frying, as shortening has a very high smoke point. Butter tends to burn too quickly.
Baking
In baking, shortening cannot replace vegetable oil in a recipe. This is because shortening is considered a solid fat and vegetable oil is a liquid fat, exchanging one for the other will negatively affect the taste and texture of your baked good. When making substitutions for baking, it is best to substitute one solid fat for another or one liquid fat for another.
Other Substitutions
A better substitution for vegetable oil in baking is pureed fruit, like prunes, apricots or prepared applesauce. It is also possible to substitute one type of oil for another; vegetable oil can be replaced by other oils, such as canola, safflower or sunflower oil.