Fels-Naptha is old school soap that works great when it comes to stains. I had a pair of khakis that I got old chain grease on, washed them regularly about 3-4 times. Regular wash didn’t get the stain out, so I called it a bust. Then 3-months later I used a little elbow grease and Fels-Naptha, just rubbing the fabric against itself for 5 minutes, and sure enough, the grease came right out. The soap is good for plenty more as well.
[After Tanner suggested Fels Naptha for getting bike grease out of a pair of Khakis, I tried it out on some grease stained pants and it worked perfectly. It does take a bit of effort, but the results are worth it. I also managed to get rid of some pesky collar stains.--OH]