Oil stains on your clothes can come from a variety of sources -- including foods, automotive products and cooking fats. No matter the source, though, you have the best chance of getting rid of that oil stain by acting quickly. Take off the garment and -- if it's washable -- get to work treating the stain as soon as you can.
Mix a heavy-duty powdered detergent with enough water to make a runny paste. Apply the paste to the oil stain. Alternatively, pour some heavy-duty liquid detergent on the stain.
Rub the fabric together to work the paste or liquid detergent deep into the oil stain.
Launder the clothing in the hottest water that's safe for the fabric; consult the garment label to be sure. Add the recommended amount of detergent for the size of your laundry load.
Remove the garment from the washing machine and inspect the stained area. If you can still see the stain, rub more detergent paste or liquid detergent into the area, then launder it again. Repeat until the stain is gone. Don't dry the garment until the stain is gone, or the heat may set in the stain.