The rhodium(I, III)-iron(II, III)-chloride ion catalyst system for the oxidation and oxidative carbonylation of methane in the presence of molecular oxygen and carbon monoxide was developed and studied. Rhodium(III) chloride was used as a catalyst precursor, and iron(III) oxide or acetylacetonate as a cocatalyst. Reactions were carried out in a trifluoroacetic acid-water medium at 95degreesC and a total gas pressure of approximately 10.0 MPa.