The analysis of carbonyl species of a gasoline fuelled Spark-Ignition and Homogeneous Charge Compression Ignition (SI/HCCI) engine operating modes was performed upstream and downstream of a three way catalyst (TWC) converter. All data were obtained during steady-state, fully warmed-up operation at different engine conditions, using a winter grade commercial gasoline containing 2% w/w ethanol (C2H5OH). Qualitative and quantitative analysis of carbonyl compounds in exhaust gases were performed using 2,4-dinitrophenylhydrazine (DNPH)-high-performance liquid chromatography (HPLC). The major carbonyl compounds detected in the collected samples were acetaldehyde, acrolein, benzaldehyde and m-tolualdehyde. Depending on the engine operation conditions, the percentage contribution of the carbonyl compounds to the total hydrocarbons emission in this study lies between 2.7% and 5.2%. Formation of low molecular weight carbonyl compounds was more prominent when the engine operated at low load HCCI mode (low combustion temperature), while aromatic aldehydes were more significant in the case of SI mode operation, in which the combustion temperature is relatively high compared to the temperature from low load HCCI mode. Even though, the catalyst reduced the hydrocarbons emission effectively, including the carbonyls, there is no significant effect on the emission of acetaldehyde and acrolein emissions. (C) 2013 Published by Elsevier Ltd.