Try soaking the oil stain up with some cornstarch or powdery floury substance. Tapioca flour works as well etc. After keeping it on there for a while try rubbing that starch in and continue to add more to try to get as much oil soaked up. Then apply dish soap to the patch. Continue to work the dish soap into the fibers along with the cornstarch with a nail brush or toothbrush. Then wash. Good luck!
Pouring boiling (or very hot) water on the stain may also help to break it up.
This is my favorite degreaser product for getting grease and oil stains out of fabric. ( click here for the affiliate shopping link for it) I rub a little directly on the stain, let it set a few minutes then wash as normal. Works great!!
I use Dawn dish soap for oil stains on all fabrics. I use it for all grease stains on any surface. It even takes tar off of cars. For clothes put some on the stain and let sit for a while. Use a soft brush if needed, then wash as usual. I have even gotten old stains out with Dawn.
I use Murphy's Oil soap, full strength on the spot, then throw in the washer with warm water.