TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe ability to monitoring bottomhole flowing pressure in pumping oil wells provides important information regarding both reservoir and artificial lift performance. Converting surface pressure measurements to bottomhole is currently accomplished by locating the fluid level in the annulus using a sonic device and then applying a correlation to estimate the density of the gas-cut liquid column above the perforations. This gascut liquid column exhibits Zero Net Liquid Flow (ZNLF) conditions where the casing head gas flows through a nearly stagnant liquid. A review of literature reveals that the correlations currently in use by the industry are based on low pressure and low viscosity data. Increasingly, operators are encountering high viscosity fluids and in some instances, casinghead gas flows into gathering systems which are not the typical low pressure systems. This paper presents recent experimental measurements for ZNLF under high viscosity and pressure conditions. The results indicate that viscosity and pressure have a significant effect on the calculated bottomhole pressures and that these effects are not accounted for in the currently applied methods. New methods are presented to calculate multiphase density, i.e. gradient correction factor, under high viscosity and high pressure conditions.