Flow patterns for horizontal intube flow boiling have been studied for the new refrigerants HP80 and HP62 and the conventional refrigerant R-502. The flow pattern observations were compared with several criteria utilized in horizontal flow boiling correlations for determining whether the entire circumference of a horizontal evaporator tube is all wet or only partially wet. Use of only the liquid Froude number FrL (utilized by numerous flow boiling correlations) is shown to be completely unreliable. Stratified (partially wet wall) flow was found to occur at Froude numbers up to 16 times those of the recommended threshhold values utilized by the correlations. A semi- empirical method for predicting stratification proposed by Klimenko and Fyodorov is an improvement but is only patrially successful in predicting the present data.