In this study, Response Surface Methodology (RSM) in combination with Box-Behnken Design (BBD) was used to optimize the temperature, catalyst loading, and blending ratio for a co-gasification process. The catalytic co-gasification of coconut shells (CS) and oil palm fronds (OPF) blends was performed in the presence of cement, dolomite, and limestone catalysts. A combined effect of temperature, catalyst loading, and blending ratio on production of H2, CO, and tar formation was investigated by using a BBD approach. The results showed the strongest influence of the process temperature on H2 and CO yield, and tar formation followed by the catalyst loading and blending ratio. A catalyst loading of 30 wt, process temperature of 900 °C and blending ratio of CS50:OPF50 were predicted as the optimized conditions for the reported co-gasification results. The highest H2 yield of 20.64 vol was produced during catalytic co-gasification of the blended biomass with limestone followed by the cement (18.22 vol) and dolomite (14.99 vol). Under optimized process conditions, lowest tar concentration of 0.87 g/Nm3 was obtained with limestone follow by the cement (1.42 g/Nm3) and dolomite (2.13 g/Nm3). However, blending ratio did not affect H2, CO yield, and tar formation appreciably. Conclusively, the mixing ratio of CS and OPF would have a negligible role in controlling the process output. © 2018 Energy Institute