One of the VIPs that Audi invited to be present at the launch of the Mileage Marathon in New York on Monday was Sylvia Williams. Williams is the general manager of business development for future fuels at Shell. The main topic of interest in New York was GTL fuel. GTL is a synthetic liquid diesel fuel made from natural gas. The catalytic process used is similar to that used by companies such as Coskata that are producing cellulosic ethanol from a syngas generated from biomass. The #8 A4 that my friend Lou Ann Hammond drove from New York to Chicago started off the trip with a full tank of GTL. Unlike conventional petroleum diesel - and to a lesser extent biodiesel - GTL is completely clear, colorless and odorless. Since it contains no aromatic compounds it burns cleaner and actually produces dramatically less soot and fewer NOx emissions as well. Currently, GTL isn't available in North America but Shell sells a 10 percent GTL blend in Europe as a premium diesel under the V-Power brand because it also helps engine performance. One big advantage of GTL is that it can be used and distributed without any infrastructure or engine changes. It is however, more expensive than petroleum diesel. Check out Lou Ann's video interview after the jump.