An improved two-phase flow pattern map is proposed for evaporation in horizontal tubes. Based on new flow pattern data for three different refrigerants covering a wide range of mass velocities, vapor qualities and heat fluxes. The new flow pattern map includes the prediction of the onset of dryout at the top of the tube during evaporation inside horizontal tubes as a function of heat flux and flow parameters and is an extension to the flow pattern map model of Kattan et al.(5). The modifications proposed allow an accurate prediction of the flow pattern for very different fluids which are the substitute refrigerants (HFC- 134a and HFC-407C) and the natural refrigerant R-717(ammonia).