Gasification of petroleum coke can present a problem with ash accumulation inside a gasifier because of the high melting temperature of V2O3. For slagging of V2O3 it was proposed to mix petroleum coke and Korean anthracite. The ash viscosities of two domestic anthracites (government reserve coal mix and Jangsung anthracite) were determined, along with the necessary flux concentrations. Both coal ashes had very high viscosities, and although both CaO and dolomite were effective in lowering the viscosity, dolomite was more effective than lime. V2O3 in coke ash remained solid at typical gasification temperatures, and the solid V2O3 caused the slag viscosity to increase. Slag equilibrium calculations were carried out using FactSage. The difference between experimentally determined T-cv and T-liq predicted by FactSage was less than 20 degrees C, when the accurate ash composition was provided, proving that T-cv can be estimated by T-liq. Using calculated T-liq, the amount of flux necessary was determined for a given minimum gasification temperature and coke:coal mixing ratio. In order to keep the flux concentration to a minimum, it is recommended to use a 90:10 mixture of coke:Jangsung coal with dolomite flux and to operate the gasifier at a temperature above 1370 degrees C. (C) 2008 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.