The Technical University of Denmark, DTU, has constructed, built and tested a gasifier [1, 11] that is fueled with wood chips and achieves a 93% conversion efficiency from wood to producer gas. By combining the gasifier with an internal combustion engine and a generator, a co-generative system can be realized that produces electricity and heat. The gasifier uses the waste heat from the engine for drying and pyrolysis of the wood chips while the produced gas is used to fuel the engine. To achieve high efficiency in converting biomass to electricity it necessitates an engine that is adapted to high efficiency operation using the specific producer gas from the DTU gasifier.So far the majority of gas engines of today are designed and optimized for SI-operation on natural gas. The presented work uses a modern and highly efficient truck sized natural gas SI-engine at Lund University, Sweden, that has been converted to HCCI operation to investigate efficiency, emissions and general performance while operating on producer gas. The results are also compared with natural gas operation. Producer gas has been proposed as a possible HCCI fuel in former publications  but was never used with the current gas composition from the Viking gasifier.