Measurements of two-phase flow pressure drop have been made during a phase-change heat transfer process with refrigerant (R-134a) as a working fluid for a wide range of pressures right up to the critical pressure. The experiments were conducted in a uniformly heated vertical tube of 12.7 min internal diameter and 3 m length over a heat flux range of 35-80 kW/m(2), mass flux range of 1200-2000 kg/m(2) S, exit quality range of 0.19-0.81 and for reduced pressures ranging from 0.24 to 1 with a fixed inlet subcooling of 3 degrees C. The measurements were compared with the predictions from the homogeneous flow model, a separated flow model using correlations drawn from the literature for void fraction and frictional pressure drop, and finally, using a flow pattern-based predictive method accounting specifically for bubbly, slug and annular flow regimes. It was found that the best results were obtained with the flow pattern-based approach with a mean deviation of 20% over the entire pressure range. (c) 2006 Elsevier Ltd. All rights reserved.