An equilibrium assemblage of olivine, Ca-free pyroxene, and PtFe alloy can be used to calculate oxygen fugacity at a known temperature and pressure. This oxygen geobarometer has been tested T = 1300-1450°C, P = 1 bar and 10 kbar. The calculated log $$fO_{2}$$ may be compared with that determined by the $$CO_{2}-H_{2}$$ mixture used to control the furnace atmosphere in the 1 bar experiments and, in the case of the 10 kbar experiments, the log $$fO_{2}$$ determined from the graphite-fluid equilibrium. The average deviation of the calculated log $$fO_{2}$$ and that determined by other means is 0.2; the maximum absolute difference is 0.4. The distribution coefficient ($$K_{d}$$) for Fe and Mg between coexisting olivine and pyroxene was found to range from 1.14 at $$X_{Fe{2}SiO_{4}}^{ol} = 0.164$$ to $$X_{Fe{2}SiO_{4}}^{ol} = 0.655$$, and varies systematically with the Fe/(Fe + Mg) of the phases.