After replacing the spark plugs in the truck and having driven enough miles to calculate the improvement. My truck went form 18.1 MPG to 18.6 MPG. So, given my truck holds 40 gallons, That equates to 1/2 mile per gallon improvement or 20 miles more per tank load. That comes to 1040 more miles per year regardless of price off gas or a savings of 55.91 gallons in a year. Given I will change my plugs every 6 years, that means I should save 335.46 Gallons.(at the same miles driven per year). Concourse always does a great job and having your car/truck serviced does pay off. Thanks guys. Mike