Put cardboard inside the pants so the following steps won’t just move the stain to the back side of the pants. Spray the spot with WD-40 to release the oil. Then form a paste of blue Dawn dishwashing liquid and baking powder. Scrub the spot with that paste using a toothbrush. Scrub it really well, occasionally blotting the area with a clean towel. Then toss the pants in the wash. If some of the stain remains, repeat the process. This really does work. This works even on set in stains.