Friction between moving parts in engines burns fuel. Generally less friction means you will save on gas. So better lubricants could improve your gas mileage. Roil Platinum is an oil additive which seems to do a pretty good job on fighting friction based on the video below. You might want to try it out and see what happens. You will have to do careful measurements of fuel consumption before and after to be sure. The best is to have a real time fuel consumption gauge, such as the ScanGauge.