What can I substitute for vegetable oil in a recipe?
On first blush, you will probably want a fat or oil with similar qualities as the "vegetable" oil you're replacing, such as olive oil. Butter has a much lower a smoke point, however, cornbread recipes exist that use butter or lard. I'd be willing to experiment, particularly if you're used to cooking with butter. (Just be careful with heat.) As far as quantity, I'd use a bit less than 1/3 of a cup, but that's me being defensive as I don't know the recipe you're using.