Two model bio-oil fractions were chosen as two different major classes of components present in bio-oil. Steam reforming of the two fractions was carried out to investigate the gas product distributions and carbon deposition behavior. Higher H-2 yield and carbon conversion to the gaseous phase can be obtained at relatively low temperature (650 degrees C) for steam reforming of the light fraction. For steam reforming of the heavy fraction, a higher temperature (800 degrees C) is necessary to obtain higher H-2 yield and carbon conversion to the gaseous phase. At 800 degrees C, the heavy fraction requires a higher steam to carbon ratio (10) than that for the light fraction (7) to achieve efficient steam reforming. Based on the same carbon space velocity, for 10 h stream time, the drop of H-2 yield and carbon conversion to the gaseous phase in the steam reforming of the heavy fraction is more rapid than that of the light fraction. Carbon deposition in the steam reforming of the heavy fraction is much more severe than that of the light fraction, as determined by carbon content analysis and SEM detection.