It is necessary to utilize waste cooking oil as a raw material of biodiesel because the land area available for cultivation in Japan is limited. Waste cooking oil also includes long-chain saturated compounds and free fatty acids derived from animal fats. The former has a high freezing point and the latter forms a soap with the alkali catalyst typically used in biodiesel production, reducing the yield. To make waste cooking oil available for biodiesel production, pyrolysis of the waste oil was attempted. The resulting triacylglycerols were found to decompose at 360 to 390 degrees C, fatty acids were generated by cleavage of the ester bond, and short-chain hydrocarbons and short-chain fatty acids were generated by cleavage of the unsaturated bonds in the hydrocarbon chain. When the retention time was extended with a reaction temperature of 420 degrees C, light-oil hydrocarbons were generated by decarboxylation of the fatty acids. By adding palladium supported by activated carbon (Pd/C) as a catalyst, decarboxylation was promoted, and hydrocarbons comparable to light oil were selectively obtained in high yield at 85 wt.%. Compared to the biodiesel obtained by transesterification, the biodiesel obtained by pyrolysis showed improvement of about -5 degrees C in the pseudo-cold filter plugging point. (C) 2011 Elsevier B.V. All rights reserved.