The present study is an attempt to investigate a syngas-diesel dual fueled diesel engine operation under varying load conditions from the second law point of view. The fuel type in dual fuel operation is achieved by varying the volumetric fractions of hydrogen (H2) and carbon monoxide (CO) content in syngas. It is revealed that increasing the hydrogen quantity of syngas increases the cumulative work availability and reduces the destroyed availability. This enhancement is due to a better combustion process and increased work output when a high amount of H2 quantity is employed. At lower loads, the in-cylinder combustion temperatures are reduced in case of the dual fuel combustion. Hence, the destruction availability is increased due to poor combustion and reduced heat transfer availability losses. When the engine is operated beyond 40% load, the destroyed availability reduced due to higher combustion temperature and pressure. The increase in the both exhaust gas and cooling water availabilities are reflected in an increase in second law efficiency with increasing load. The dual fuel cumulative work availability is increased at higher loads and thus, the exergy efficiency is increased. © 2010 Elsevier Ltd.