Description Mobil 1 High Mileage is an advanced full synthetic motor oil designed to help extend engine life of vehicles with over 75,000 miles. Mobil 1 High Mileage motor oil features a boosted level of seal conditioner to protect engine seals because, over time, rubber seals can harden or shrink, resulting in oil leaks. If your engine contains excessive sludge deposits due to less-than-adequate maintenance practices, Mobil 1 High Mileage synthetic motor oil can help reduce this sludge.