Although a variety of precursors have been proposed for the formation of high molecular weight hydrocarbons (HMWHCs) in crude oil, their precise origin remains elusive. Quantitative studies of macrocrystalline wax and microcrystalline wax content of source rock extracts from the Damintun depression, Liaohe Basin, a typical high wax producing area, coupled with microscopical maceral composition studies and pyrolysis-GC analysis indicate that oil shale enriched in lacustrine biomass makes a primary contribution to wax in oil. The main precursors of high wax oil are lacustrine alginites and their amorphous matrix, which are highly aliphatic in nature and have high generative potential for HMWHCs. Wax generation efficiency could be affected by organic material abundance and maturity. The high abundance and low maturity of organic material are favorite for the formation of high quantity of wax, which declines with decreasing organic abundance and increasing thermal maturity. This suggests that wax is derived from organic-rich lacustrine biomass at early stages of maturation (RO = 0.4%-0.7%). Although the contribution of high plant cuticular wax and sporopollen cannot be ruled out, lacustrine biomass is more important in the formation of high wax oil.