Intube flow boiling experiments for two new zeotropic refrigerant mixtures and R-502 have been carried out at three saturation temperatures over a wide range of local vapor qualities. The zeotropic mixtures tested were HP80 and HP62. Local flow boiling coefficients for HP62 are slightly larger than those for R-502 under the same test conditions while those for HP80 are slightly smaller. The heat transfer performances of the three fluids are generally quite accurately predicted by an existing flow boiling correlation modified here to include a nucleate boiling mixutre equation. However, in the post dryout regime at high vapor qualities the measured coefficients are much lower than those predicted.