A mechanism and kinetics to describe the catalytic upgrading of a biomass-derived raw gas is provided in this paper. The mechanism encompasses the principal trends in the evolution of tar and light hydrocarbons. Using this mechanism and a pseudotar that represents tar and light hydrocarbons formed in situ, a kinetic model is developed. The applicability of the kinetic model is demonstrated for a process activated ilmenite. The experiments were conducted in a bench-scale, bubbling fluidized-bed reactor that was fed with a tar-rich raw gas stream from the Chalmers indirect biomass gasifier. The effects of the ilmenite on tar decomposition and total gas composition were evaluated at 800 degrees C for three different gas solid contact times. Combing the experimental results and the proposed kinetic model, the evolutionary profiles of the different tar and light hydrocarbon groups can be evaluated in relation to the gas solid contact time. The results form the basis of a process model for optimization and upscaling.