J.S.
If it is a washed in black or brown automotive or bike grease try this...rub Crisco into stain, it will begin to dilute the black gunk in the fibers, then wash out with D.. BTW this also works with kids and permanent marker...only use Eucerine or other heavy oily lotion instead of Crisco, it seems to get into the kids pores and lift the stain a little, then wash off with D. and soak them in the bathtub.