Thermogravimetric analysis (TGA) has been used to investigate the carburization kinetics of Mo-W sulfide using an H-2:C3H8 feed mixture. The effect of heating rate over the range 1-10K min(-1) showed that up to four different carburized products may be formed but the critical (peak) temperature for formation of these species and the amount (peak height) of each species formed are highly dependent on the heating rate employed. The critical temperature increased linearly with heating rate for each of the four products. The four TGA peaks corresponding to the four phase transformation species are consistent with XRD identifiable species, namely; alpha-Mo2C, beta-Mo2C, W and MoC1-x. Isothermal conversion-time data at three different temperatures are described by a reaction-controlled shrinking core model implicating a first-order dependency on the H-2:C3H8 ratio. The reaction exhibited fractional order dependence on the metal sulfide concentration, the associated global activation energy estimated as 227 kj mol(-1) is representative of a non-catalytic gas-solid reaction. (C) 2004 Society of Chemical Industry.