A single one-lump first-order reaction for the catalytic elimination of tar present in the flue gas from biomass-fluidized bed gasifiers is not good enough for some applications. A new and more advanced reacting network and microkinetic model has been generated and is here presented. It is based on two lumps, the more and the less reactive tar species, and has four kinetic constants. Each lump reacts (disappears) by both catalytic and thermal reactions. The microkinetic model is applied to results obtained at around 840 degreesC and at small pilot plant level with two very different solids: silica sand and a commercial (ICI 46-1) nickel-based steam-reforming catalyst. The values found for the four kinetic constants are self-consistent, fit well the results, and mean a clear step forward in the modeling of the catalytic tar abatement.