The flow regime map presented uses dimensionless correlating parameters and allows for the accurate prediction of the occurrence of the stratified roll wave regime in horizontal two-phase pipe flow. Transitional boundary relationships that delineate the roll wave regime from other neighboring patterns, such as the stratified ripple and film plus droplet conditions, are given. The two-phase data followed a relationship that was dependent only on the map correlation parameters and the superficial liquid velocity. This map, together with recent developments by others [e.g., Watterson et al., Ind. Eng. Chem. Des., 2002, 41, 6621 and DeV. Chem. Eng. Min. Process., 2003, 11, 107; Spedding and Cooper, Int. J. Heat Mass Transfer, 2002, 45, 219; Spedding et al., DeV. Chem. Eng. Min. Process. 2003, 11, 95] allows for prediction of the major two-phase parameters, such as holdup and pressure drop, for the stratified roll wave regime.