One of the major problems for biomass gasification is the presence of tar in the product gas. We are presently investigating catalytic behavior of olivine as a prospective bed additive for biomass gasifiers for tar removal. The present investigation is a continuation of our work using pretreated olivine as a tar removal catalyst, and the effect of different gas components is described in this paper. H2O, CO2, and H2 have a strong influence on naphthalene decomposition reactions. H2O and CO2 have an enhancing effect, and H2 has an inhibiting effect. Kinetic parameters were determined in the presence of the main gas components from a gasifier using a simple power law kinetic model, and an activation energy of 213 kJ mol-1 was found over pretreated olivine as the catalyst. An attempt is made to postulate the reaction network for naphthalene decomposition in the presence of a reactive gas mixture.