Boiling heat transfer data from a natural circulation single tube reboiler, for three binary liquid mixtures, have been obtained for a variety of concentrations. Mixtures of iso-propanol, n-propanol and glycerol each with water were tested. Two tubes, one in copper and one in stainless steel, were used to obtain length-mean heat transfer coefficients. Also one stainless steel tube designed to give local heat transfer coefficients was employed. All the tubes had nominal dimensions of 0.5 in. diameter and 4 ft. length. In correlating the experimental data it has been found that the single-component correlation is adequate provided that the surface tension used in it is that of the binary liquid of the interfacial concentration σ* L, and that the temperature driving force is the difference between the wall temperature and the saturation temperature of the mixture of the interfacial concentration. The latter is found by correcting the apparent temperature difference ΔT f with the correction factor F. The length-mean coefficients corresponding to a combination of flow boiling regimes with the exclusion of the purely bubbly-nucleate and dry wall regimes have been correlated by the equation h TP h L =0.065 ( 1 X tt ) ( T sat Δ T f ) ( σH 2O σ* L ) 0.9 F 0.6 where the factor F = [ 1 − ( y* − x) ( C L h fg ) ( α D ) 0.5 ( d T d x )] 75% to 95% of the data points, depending on the type of mixture, are within the ±20% accuracy limits. The point coefficients are correlated by the same equation within ±30% accuracy limits if some of the data points, where there is suspicion of the predominance of nucleate boiling or dry wall regimes, are rejected. The factor F is a powerful parameter with binary mixtures having a highly non-ideal vapour—liquid equilibrium relationship. In the case of the binary mixtures of low relative volatility this factor is very close to unity.