As your Authorized AMSOIL Dealer in San Marcos, Synthetic Oil Inc. is dedicated to providing the ‘Heart of North County’ with the world’s best synthetic lubricants. Synthetic Oil has proudly served the entire San Diego metropolitan area for over 30 years. From the daily commutes near California State University San Marcos (CSUSM) to the heavy traffic along the Highway 78 corridor, our AMSOIL motor oils and filters are engineered to protect your engine against the unique heat and stop-and-go demands of the inland valleys. Beyond automotive care, we specialize in high-performance Marine, Motorcycle, and Off-Road lubricants, ensuring your boat, bike, or 4×4 is ready for the Pacific or the North County trails. Shop online for factory-direct shipping straight to your San Marcos doorstep.