The air gasification of palm waste specifically palm kernel shell has been performed in the fixed bed gasifier using coal bottom ash as a potential catalyst. Effect of the process variables (temperature, catalyst loading, and airflow rate) has been investigated on the product gas composition. The design of experiments was accomplished using the Design Expert v11® with a Central Composite Design approach. Moreover, the parametric study and optimization of the entire process have been carried out using Response Surface Methodology within the specific range of variables. The results suggested that the temperature has been found as the most influencing parameter for increment of H2 and CO production. Whereas, airflow rate was more sensitive for CH4 and CO2 production. Catalyst loading was found very effective for the amplified amount of H2 and CO production and the reduction in the amounts of CO2 and CH4, caused by the catalytic activity of coal bottom ash (CBA). Optimized parameters are found to be the temperature of 850 °C, catalyst loading of 14.50 wt, and airflow rate of 2.50 L/min, which predicted the composition for H2 of 31.38 vol, CO of 26.44 vol, CH4 of 15.67 vol, and CO2 of 25.59 vol. © 2019 Elsevier Ltd