Castrol GTX High Mileage 10W-30 is the #1 consumer high-mileage brand of motor oil. It's a synthetic blend engine oil that helps extend the life of engines by protecting against sludge, wear and burn-off. Engineered with Phosphorous Replacement Technology, it also protects emission systems by replacing some of the phosphorous that can damage catalytic converters. Meets or exceeds the following specifications: API SP/SN PLUS/SN/SM, ILSAC GF-6.