Preheat oven to 425°.
Line or butter a 12 cup muffin tin.
Melt the butter and pour into a mixing bowl with vegetable oil, granulated sugar and brown sugar. Mix together with a wooden spoon.
Stir in milk, eggs and vanilla.
Add flour, baking powder, baking soda and salt. Stir just until combined, it is okay if there are a few lumps.
Fold in chocolate chips.
Bake for 15-17 minutes or until a toothpick inserted comes out clean.
Run a sharp knife around the muffins if you are not using liners. Remove muffins to a wire rack to cool.