Over the last decade, the development and deployment of in-line multiphase flow metering systems has been a major focus worldwide. Accurate measurement of multiphase flow in the oil and gas industry is difficult because it occurs in wide range of flow regimes and multiphase meters do not generally perform well under the intermittent slug flow conditions which commonly occur in oil production. A novel ultrasonic multiphase metering concept has been proposed and investigated which measures the flow rates of the liquid and gas phases from ultrasonic measurements made in two different flow regimes – partially separated and homogeneous — in the same measurement system and fuses the data from the different flow regimes to obtain improved overall measurement accuracy. The system employs a partial gas/liquid separation using a T-junction configuration and a combination of Doppler and cross correlation. The partially separated flow regimes uses ultrasonic cross correlation measurement for the liquid flow measurement which has gas entrained within it. The homogeneous regime employs ultrasonic Doppler method. This approach has been tested on water/air flows on a 50mm facility in the Department of Process and Systems Engineering. The liquid and gas flowrate measurements using the proposed techniques were compared with a reference measurement and good agreements between these two measurements were obtained with error ranging from ± 2% and 10%, respectively. Such a performance offers the potential for an in-line multiphase flowmeter with improved performance.