Introduction Mass density, because of its linear relationship with porosity, has long been recognized as a potential seismic indicator of fluid saturation. Given its dependence on mineral composition, density can also be diagnostic for lithology. In this chapter, we discuss some key aspects of a wide-angle processing and density inversion workflow and apply it to a bitumen reservoir in Canada for imaging reservoir heterogeneities (e.g., shales) that can potentially act as permeability baffles. In this field, intrareservoir shales typically have higher densities than surrounding reservoir sands. This wide-angle workflow yields stable density estimates, from reflected P-waves alone, at a resolution suitable for mapping the intrareservoir shales. This study is based on data from the Surmont bitumen reservoir approximately 60 km southeast of Fort McMurray, Alberta, Canada, in the Lower Cretaceous McMurray formation. The oil is too deep (400 m) to mine. Steam-assisted gravity drainage (SAGD) technology is being used to inject steam into the reservoir and heat the oil so that it can be produced. Shale heterogeneities within the reservoir (Figure 1) thicker than 3 m could have an impact on steam chamber development and affect SAGD performance. Predicting the areal extent and the thickness of these bodies would lead to better reservoir management.