An experimental study of pressure drop in forced convection vaporization has been made in a heat transfer loop designed for the investigation of local heat transfer coefficients and local pressure gradients for water flowing vertically upward in an electrically heated tube. Data presented are for ⅛-in. i.d. 347 stainless steel tubes of 15 and 20-in. lengths with mass fluxes of 200 to 700 lb/sec ft2, heat fluxes of 1 to 8 × 105 Btu/hr-ft2, qualities at the exit up to 50% and with pressures ranging from 50 to 400 psia. A correlation of the local pressure gradients as a function of the Martinelli parameter Xtt has been obtained to within ±15% and a design procedure for calculating over-all pressure drop from this correlation is suggested.