Why oil is different from dirt
Concrete is porous. Dirt and organic growth sit largely on the surface, which is why they clean off. Oil soaks in — it moves down into the pore structure of the slab, sometimes several millimeters deep.
Pressure alone only addresses the surface. You can blast the top layer clean and watch the stain reappear as oil wicks back up from below, which is exactly what happens when someone pressure washes an old stain without treating it first.
What actually works
Degreasers and emulsifiers. A degreaser applied to the stain breaks the oil's bond with the concrete and lifts it up out of the pores so it can be rinsed away. Dwell time matters — the product needs to sit and work.
Heat helps significantly. Hot water pressure washing is meaningfully more effective on oil than cold, because heat thins the oil and helps it release.
For severe or long-set stains, poultice treatments — a paste that draws oil out of the slab as it dries — can pull out more than surface cleaning reaches. It's slow and often needs repeating.
What results to actually expect
Fresh oil, days to weeks old: usually removes well.
Months old: substantial improvement, often close to gone.
Years old, repeatedly deposited in the same spot — the classic under-the-engine stain: expect meaningful lightening, not disappearance. The concrete has absorbed oil throughout its depth in that area.
Anyone who looks at a decade-old black patch under where a car has parked and promises it'll look like new concrete is telling you what you want to hear.
Preventing the next one
Clean spills quickly — cat litter or an oil absorbent, then a degreaser, within days rather than months. Sealing a concrete driveway substantially reduces absorption and makes future spills far easier to clean. A drip pan under a vehicle you know leaks is unglamorous and completely effective.