There are currently over 3,500 oil and gas structures in the northern Gulf of Mexico. Platform operations and their prior drilling operations produce trace amounts of lead, barium, vanadium, and lanthanum residues that are leached into the surrounding waters and are deposed on the sea floor. These residues have isotopic ratios different from those typical of the Gulf seafloor and can be used as "markers" if they become incorporated into hard-parts, such as otoliths, of fishes associated with oil and gas platforms.