I have a 2003 Bonneville with over 200k miles on it.Owned it since new, it has the 3800 engine. Have used Mobil 1 on most of the oil changes. Well, the engine started "using" about a quart of oil every 3 months about a year ago. I saw Mobil 1 High Mileage on the shelf and tried it. Runs great on it and "uses" less oil than it did on regular Mobil 1. I would guess a 50% improvement.