The experimental study was carried out on anaerobic digestion of jatropha (Jatropha curcas) and pongamia (Pongamia pinnata) oil seed cakes in a 20 m(3)/d capacity floating drum biogas plant under mesophilic temperature condition. The average specific methane production potential of jatropha oil seed cake was observed as 0.394 m(3)/kg TS and 0.422 m(3)/kg VS. The average content of methane and carbon dioxide in the produced biogas over 30 days of retention time period was found as 66.6% and 31.3%, respectively. Cumulative methane yield over 30 days of retention time period was found as 131.258 m(3) with a 259.2 kg of input volatile solids, with an average total volatile solids mass removal efficiency of 59.6%. However, in case of pongamia oil seed cake average specific methane production was observed as 0.427 m(3)/kg IS and 0.448 m(3)/kg VS. The average value of methane and carbon dioxide content in the produced biogas over 30 days of retention was found as 62.5% and 33.5%, respectively. Cumulative methane yield over 30 days of retention time period was found as 147.605 m(3) with a 255.9 kg of input volatile solids, with an average total volatile solids mass removal efficiency of 74.9%. (C) 2010 Elsevier Ltd. All rights reserved.