Use caution when removing diesel from laundry because it makes fabrics more flammable. Additionally, it's important to wash garments stained with diesel separately from other laundry.
Pre-treat the stain
Use a solvent-based stain removal product, like Shout or Spray 'n Wash, to pre-treat diesel stains. If you don't have a stain removal product on-hand, you may also use a heavy-duty liquid detergent to treat the stain; work it in by gently rubbing.
Put the garment in the wash
Wash the pre-treated garments in the hottest water setting allowed with the regular amount of detergent. Let the garment dry if the stain disappears, but repeat the process if it stays.
Soak the stained clothes in water with 1/2 to 1 cup of baking soda and then wash and rinse as usual if you need to get rid of any lingering odors. If the garment has a particularly heavy odor, add 1 cup of non-sudsing household ammonia to a washer full of warm water and soak it for a few hours.
Take garments labeled "dry clean only" to a professional and explain the stain. Use the stain remover from a dry cleaning kit if you plan to dry clean at home.