An extraction method was used to optimize the miscibility of supercritical water (SCW) with asphaltene (AS) at 400-450 degrees C and 20-35 MPa. The optimal temperature for the determination was 440 degrees C due to the improved balance between solubility and the coking rate. With increasing the pressure at 440 degrees C, the degradative extraction yield of AS using SCW reached a maximum at around 30 MPa. The extraction behavior was thought to be controlled mainly by the water properties represented by the dielectric constant (DC) and Hansen solubility parameter (HSP). These properties affected the miscibility with AS and consequently the extraction yield. As a result, the optimal water properties to achieve the highest miscibility with AS were DC = 2.2, delta(p) = 6.4, and delta(h) = 9.7. (C) 2012 Elsevier B.V. All rights reserved.