SUPERIOR, WI --- Amsoil Inc. is now offering a money-back guarantee on its gasoline additive AMSOIL P.i. Performance Improver if the product fails to improve a vehicle's mileage.

Amsoil Inc. said field tests show that AMSOIL P.i. provides an average fuel economy improvement of 2.3 percent and up to 5.7 percent. If a customer does not see a measurable fuel economy improvement in his or her vehicle after first-time use of P.i., Amsoil said it will refund the purchase price of the product.

Amsoil said the gasoline additive increases fuel economy, reduces emissions and restores vehicle power and performance by dissolving and removing combustion chamber, intake valve and fuel injector deposits.

The P.i. money-back guarantee offer is good through December 31, 2008 and is open to everyone who drives a gasoline-powered vehicle. Because the most dramatic fuel economy improvement is achieved after first-time use of P.i. in a vehicle with accumulated deposits, the P.i. money-back guarantee is limited to vehicles with a minimum of 25,000 miles that have not previously been treated with P.i. and have not undergone any fuel system or fuel injector cleaning procedure. P.i. must be used with a full tank of gas, and the P.i.-treated gas must be run until the tank is near-empty before filling up again.

Customers are eligible for the refund if they do not see a fuel economy improvement following use of the subsequent tank of gas after P.i. treatment. If a customer has not received a fuel economy benefit and wishes to take advantage of the money-back guarantee, he or she may simply download and print the refund form from the Amsoil website at The form contains complete qualification details.