To clean oil off a garage floor, absorb the spill with absorbent pads or cat litter. Then, apply a degreaser and scrub the area with a stiff brush. Rinse with water and repeat the degreasing and scrubbing process if necessary. For larger spills, use a pressure washer with a degreasing solution. Always wear protective gear, ventilate the area, and dispose of waste materials properly. Consider using containment booms or floor mats to prevent the spread of oil and seek professional cleaning services for extensive spills.