Free convection heat transfer from a heated wire to near critical binary mixtures of R−22 and R−115 was investigated experimentally. Measurements included determination of mixture bulk temperature and pressure, wire temperature and heat flux at the wire surface, and mixture concentration. Observed heat transfer and fluid flow patterns were very similar to those known to occur in near critical pure fluids. Modest peaks in heat transfer coefficients were found at small temperature differences for all mixtures. For bulk fluid temperatures slightly below their critical temperatures boiling-like phenomena were observed and the corresponding maximum heat transfer coefficients were found to be up to 600% higher than those obtained at larger temperature differences.