Spray the wall with a dye-free degreasing cleaner. Wipe the area down with a damp sponge to remove any surface dirt, then wipe the area with a soft cloth. Let it dry completely.
Tape drop cloths down underneath the stained wall to protect your flooring.
Apply an oil-based primer with a roller over the stain. Feather out the edges a few inches beyond the stain to blend it. Let the primer dry for four hours.
Apply an oil-based paint (that matches the color of the existing paint) with a roller over the primer. Let the first coat dry for four to six hours, then apply a second coat if necessary.