There are two methods that I've found very useful when removing oil stains from fabric. You want to make sure that when you treat an oil stain that you don't want to pretreat it or wet it before hand.

An organic and environmentally friendly way is to use citrus acid (orange, lemon, etc.). Dab the oil stain with the citrus acid until it disappears and wash as usual.

If you don't have any citrus acid on hand then treat the oil stain with Shout's Triple Acting spray. Spary the stain throughly and let it sit for about an hour or even overnight (depending on the type of fabric) before washing.