Abstract: The relative amount of liquid and vapor flowing in a pipe is measured by mixing the vapor and liquid into a gaseous like single phase mixture and passing the mixture through a venturi constriction to accelerate it. The pressure drop across the venturi is measured as an indication of the velocity change which varies with the density of the mixture. Mixtures with more liquid generate more pressure drop. The average velocity of the pipe contents is also monitored to eliminate pressure drop changes that result from average velocity changes rather than density changes.