I'd give this a qualified recommendation. I've used it in combination with other products and gotten good results, but it's hard to know for sure what helped the most. Anyway, the theory makes sense. Make lubricant particles teeny tiny and they can get where regular oil molecules cant, sort of forming an extra layer between metal to metal contact areas.

the FTC has allowed zMAX to make claims that it reduces friction, increases horsepower, dissipates engine heat, and helps to improve or restore gas mileage and reduce emissions in older cars, by virtue of reducing engine deposits.

Unfortunately, you have to buy a whole package of products to get the oil additive, typically running about 40 bucks. But it seems worth it.