Ultrasonic measurements are made of a multiphase fluid (oil, water and gas) in pipe or conduits with high values of gas content in the multiphase fluid. Ultrasonic transceivers are positioned around the pipe wall in acoustic contact with the fluid system. The fluid flow is caused to move in a vortex or swirling flow with vortex inducing elements located in the pipe upstream of the transceivers, forcing the gas phase to a cylindrical area at the center of multiphase flow in the pipe, with water and oil multiphase fluid components forming an outer annular flow. Measures of cross sectional composition of the gas portion of multiphase fluid are provided based on the reflected waves from the interface. Tomographic images of the relative presence and position of the three fluid phases are also formed.