Catalytic gasification of three tars from different sources (oil refinery, Petrox; coking, Huachipato; coal gasification, Gasco) was carried out at a laboratory scale fixed bed reactor using CaO as catalyst, obtained by limestone calcination. Gasification runs were performed keeping constant the tar feed flow rate, as well as the steam concentration. The residence time, tau, was regulated through the carrier gas (argon) flow. For steam to tar ratios, R-V(o) (g/g) equal to, or larger than 3.5 and temperatures over 750 degrees C, total conversion to gaseous products was obtained; solid carbon deposition was observed at lower values of R-V(o). Gas yields and product distribution can be explained and partially predicted by extensive tar characterization, reported elsewhere. A kinetic model is proposed, which coupled with mass balances in a flowing reactor led to an expression of carbon conversion to gaseous products as a function of the operating variables, R-V(o) and tau. The data for the catalytic gasification of these tars corroborate the mechanisms proposed at earlier studies of catalytic gasification, using naphthalene as a model compound.