The Holub et al. (1992, 1993) phenomenological model for pressure drop and liquid holdup in trickle flow regime at atmospheric pressure was noted by Al-Dahhan and Dudukovic (1994) to systematically underpredict pressure drop at high pressure and high gas flow rates. In this study, the Holub et al. (1992, 1993) model has been extended to account for the interaction between the gas and liquid phases by incorporating the velocity and the shear slip factors between the phases. As a result, the prediction of pressure drop at the operating conditions of industrial interest (high pressure) has been improved noticeably without any significant loss in predictability of liquid holdup. The extended model and the comparison between its prediction and experimental high pressure and high gas flow rate data are presented and discussed.