When you use oil instead of butter, you're changing the chemistry of the brownies. Oil is a liquid fat, which means it can make the brownies more dense and fudgy. On the other hand, butter is a solid fat that adds air pockets and a lighter texture.
Now, you might be wondering which type of oil to use. Well, neutral-tasting oils like canola or vegetable oil are great options. But, if you want to add some extra flavor, you could try using coconut oil or olive oil - just be aware that they have a stronger taste.
Using oil instead of butter can also affect the shelf life of your brownies. Since oil doesn't contain water like butter does, the brownies might become drier faster. So, if you're planning to store them for a while, you might want to consider adding some extra moisture to the recipe.
