With the aim of better understanding geochemistry of trace elements in marine oil shale and its combustion residues, 23 raw samples, 17 oil shale combustion residues, and 18 selected minerals from Bilong Co oil shale are studied. Potentially hazardous trace elements in raw samples include As, B, Cd, Mo, and Se, while Se, Mo, Cd, As, Bi, and U are potentially hazardous trace elements in combustion residues. As is controlled mainly by Fe-bearing minerals. B occurs mainly in clay minerals. Cd is enriched mainly in calcite. Mo is controlled mainly by organic matter. Se is mainly controlled by P-bearing minerals.