The HCCI combustion mode features characteristics that uniquely position it to facilitate the convergence of gasoline and diesel engine technologies. The ability of HCCI combustion to accommodate a broad variety of fuels is one such characteristic. In this work the viability of a simulated biomass gas that resembles in its composition so-called producer gas is investigated. The paper reports on a single-cylinder HCCI engine's indicated performance when fuelled with the biomass derived gaseous fuels. There were two biomass gas fuel compositions used in this study. Both compositions contained the same amount of CH₄, CO₂, and N₂, and they differed by the H₂ to CO ratio; for Composition 1 the ratio was 10% to 25%, and for Composition 2 it was 15% to 20%. The indicated performance of the HCCI engine was evaluated based on in-cylinder cycle-resolved pressure measurements. Two principle operating variables investigated were the operating equivalence ratio and the air/fuel mixture inlet temperature. It was found that stable combustion can be maintained over a wide range of equivalence ratios with moderate air/fuel mixture preheating and no need for EGR dilution, hence reducing the dependence of a HCCI combustion control on EGR. It is demonstrated that the biomass-derived gaseous fuels could become acceptable alternatives for reciprocating piston engines without entering the audible knocking regime.