Measurements of total chromium and hexavalent chromium have been obtained in a laminar methane/air diffusion flame. Chlorine was added to methane in the form of methyl chloride gas. A dilution-quenching probe sampled the emissions from the flame. Particles were collected on a filter and vapor phase species were collected in impingers. All samples were analyzed for hexavalent chromium with a spectrophotometric method. The filter sample was also analyzed for total chromium by X-ray fluorescence. Total chromium added to the flame was determined by gravimetric analysis of the chromium source, chromium hexacarbonyl. Recovery of chromium of up to 64% was achieved. The addition of methyl chloride to the fuel had a dramatic impact on the speciation of the chromium emission. The fraction of hexavalent chromium increased significantly as small amounts of chlorine were added. Partitioning between phases was also altered; much more hexavalent chromium was found in the impingers as the chlorine loading increased. Equilibrium calculations reproduced experimental trends but showed strong sensitivity to the thermochemical properties of the included species, particularly CrO2Cl2.