I was wondering myself... plants use CO2. Now, more gas burned equals more CO2 (which is heavier than air... so it'll stay nearer to us in the lower atmosphere unless in the case of strong updraft). So, this more CO2 will feed more plants down here on our level. That means more and better crops, more and better trees, and generally a greener ecosystem... hmm... So, here's what I wonder... How much of my extra throttle travel is going into making the corn grow better to make the ethanol that helps fuel my car? Also, to the guy who says we're running out of oil... When was the last time that you were down underground about 35,000 feet or so? Now if you say that production of fuels is getting outpaced by demand, that's within reason of an economist to say, but to say we are running out would require knowledge that even the most well educated scientists couldn't reliably attest to. To get back on topic, the best thing in my mind to increase mileage of engines is to reduce friction through different engine designs, and better spec'ed engineering in order to reduce parasitic energy loss. We have to remember that there IS a ceiling to how much energy can be squeezed out of gasoline (or any fuel for that matter). When molecules are broken apart, they release energy which we harness in a combustion pressure reaction. If we were to be able to reduce friction to a theoretical zero, we would still have a finite ceiling as to how much energy can be squeezed from a quantity of fuel. The best thing to do is work on both ends of the equation to get a better result overall. Here's a little wikipedia article about the energy content of common fuels. http://en.wikipedia.org/wiki/Gasoline#Energy_content This hypermiling BS is downright dangerous, and I have read articles advocating extreme close tailgating, and odd fuel cutoff switches to conserve fuel going downhill. The amount of time spent on this sort of thing could be better spent making up the extra money saved by working a bit more, or working to develop an actual solution to the energy source dilemma.