Asphaltene transformation in SCW (Supercritical Water) and SCW+NaOH experiments were conducted in autoclaves with sealed gold tube reactors to investigate the effect of NaOH, reaction time (0-120 min) and temperature (400-450 degrees C) on asphaltene transformation. The results showed that asphaltene transformation in SCW+NaOH gave higher asphaltene conversion, maltene yield and coke yield but less gas yield compared with those in SCW at 400 degrees C during 120 mm. Moreover, a longer reaction time and higher temperature could enhance asphaltene reactivity but led to secondary decomposition of maltene and the formation of more gas and coke in SCW+NaOH. Kinetic analysis indicated that asphaltene transformation in SCW and SCW+NaOH both fit first-order kinetics adequately. Furthermore, a three-lump kinetic model considering parallel reactions from asphaltene to maltene + gas to coke and the consecutive reaction from maltene + gas to coke was proposed to explain the effect of NaOH and temperature on asphaltene transformation. Selectivity analysis of the products implied that asphaltene transformation in SCW+NaOH at 425 degrees C was better than transformation in SCW+NaOH at higher temperatures or in SCW in minimizing coke formation. (C) 2014 Elsevier B.V. All rights reserved.