My wife used Dawn dishwashing liquid soap. It seemed to do the trick. But like many other stains, you might have "set" the stain now depending on what things you've done already.
We've found oxiclean to be a miracle for a lot of stuff. Put a little scoop in a couple gallons of hot water and soak the stained item. Works on a lot of stains. Dawn is good for grease removal too. If it was really bad I'd try my driveway degreaser spray as a last resort but warning I've never actually tried that on clothes, you might not have much luck.