Asphaltenes and maltenes from a tar sand bitumen were characterized by gross properties and /sup 13/C-nmr spectroscopy. While differences between average properties are detected, the gross hydrocarbon structure of the two fractions is virtually identical. Hydropyrolysis was used as a conversion reaction to examine the chemistry of the respective components of the bitumen. Hydropyrolysis converts bitumen to lower average molecular weight liquid products and gases with virtually no coke. Compared to the maltenes, asphaltene species contribute disproportionately to the gaseous and heavy liquid yields, but similarly to the asphaltenes found in the liquid products. Molecules comprising the asphaltene fraction from bitumen are suggested to have average molecular weights in the mid to high hundreds and are broadly distributed with respect to molecular weight, aromaticity, and heteroatom content. Molecules comprising the maltene fraction, while of a lower average molecular weight, aromaticity and heteroatom content, are also broadly distributed and there is substantial overlap between asphaltenes and maltenes with respect to these chemical functionalities. This conclusion is supported by the results of the hydropyrolysis conversion. The results of this study indicate that characterization of bitumen according to compound types is chemically more definitive and more likely to be useful for elucidating conversion mechanisms than are characterizations based on asphaltene content or structure.