Other day I changed my rear brakes, while I was at it I cleaned off one of my wheels that had been on the front when a CV boot failed. So I had this puddle of grease, degreaser, whatever other junk was on the ground on a damp day (I'm at the bottom of a hill where other garages are, everything collects here) and gravel to get it good and mushy for me. So what did I do? Planted a knee right in it when I put the wheel back on.
I have the hand cleaner that I would have used if I thought of it at the time. I grabbed the green bottle (I think its spray n wash or resolve, forget which) and the usual mix of costco powder (still not halfway through the box after 3 years, so far its cost us well under $5/year) and a small amount of oxy clean in the basin (I think its going on $6/year for same length of time). I don't care what you say, oxy clean is good for me. Those pants came out at least as clean as before I kneeled in the grease. Clean enough to wear to the office, It's on dark jeans but they're clean enough wife & i couldn't find any stains afterward.
One thing, if you don't get a stain out the first washing, DO NOT PUT IT IN THE DRYER. That's basically the worst mistake I've ever made. I'm sure pretty much any of the solutions above would work as well as mine, but the dryer will ruin your chances if you have to do it a second time.