Shortening can be melted and used in the place of oil in some recipes in the same amount of oil as requested in the recipe. Shortening should not be used in the place of oil when baking, however, because it changes the consistency of the finished product.
Although both shortening and oil are fats, shortening is a type of oil that is solidifies at room temperature. Shortening is added to baked goods to inhibit the formation of gluten. Shortening gives baked goods a lighter, spongier texture than what oil could provide. When frying food, however, shortening and oil are completely interchangeable.