Castrol® GTX® High Mileage 10W-40 is the #1 consumer high-mileage brand, specially formulated for vehicles with over 75,000 miles. It's a synthetic blend motor oil that helps extend engine life providing Superior Protection in 7 Critical Areas including corrosion prevention, sludge control, timing and friction wear. It also contains a proprietary additive to protect the emisssion system. Our Phosphorus Replacement Technology reduces harmful phosphorus to protect the catalytic converter and help extend the life of your high mileage vehicle.