The steam gasification and co-gasification reactivity and kinetics of coconut shells, oil palm shells and bamboo guadua were studied from an isothermal thermogravimetric analysis, with temperatures ranging from 750 degrees C to 900 degrees C, and steam partial pressures from 3 to 10 kPa. In the analyzed experimental range, inorganics were identified as the most influential parameter in biomass reactivity and kinetics. Accordingly, a new modeling approach is proposed to predict the gasification behavior of lignocellulosic agrowaste based on their inorganic composition. A good agreement between the experimental and modeled data was found, showing that the proposed approach is suitable for the description and prediction of the gasification behavior of biomasses with different macromolecular structure and within a wide range of inorganic composition, and H/C and O/C ratios near 1.5 and 0.8 respectively. This kinetic model could constitute a valuable tool for reactor design and scale-up of steam gasification facilities using tropical lignocellulosic feedstocks.