Sugars are the largest sustainable hydrocarbon resource on earth. About 75% of biomass consists of the inedible sugar polymers cellulose and hemicellulose , and about 10 11 kg of sugars are produced on land each year . As shown on the left side of Fig. , sugars can have a variety of structures: (1) they can be pentoses with the formula C5H10O5 or hexoses with the formula C6H12O6; in either of these cases they can adopt a furanose configuration with a C4O ring or a pyranose configuration with a C5O ring; and (3) in the case of hexofuranoses the two non-ring carbons can form two C1 side-chains or one C2 side-chain. Unfortunately-from the perspective of fuels-in all cases they are heavily functionalized with hydroxy groups, so they are solids with melting points (Tmelt) > 100 °C. However, if one of the hydroxy groups is converted to a carbonyl group and the others are removed, then the products are the liquid lactones on the right side of Fig. .