The growing demand for hydrocarbon production has resulted in improved oilfield management using various control and optimization strategies. These strategies increasingly require downhole equipment to obtain real-time oil and gas production rates with sufficient spatial and temporal resolution. In particular, downhole multiphase metering can improve the production of horizontal wells by allocating the zones of oil, gas and water inflow. However, the existing downhole multiphase meters are expensive, inaccurate or accurate only within a limited operating range and therefore such monitoring is unrealistic.To overcome these problems one can use the so-called multiphase soft-sensors, i.e. estimating flow rates from conventional sensors (e.g. pressure gauges) in combination with a dynamic multiphase flow model. This methodology uses inverse modeling concepts to estimate flow rates that are not measured directly. Based on the analysis of the transient pressure response due to a rapid inflow, a real-time estimator is proposed, which uses a dynamic model of the multiphase wellbore flow and information from conventional pressure sensors. The feasibility of the proposed concept is assessed via simulation-based case studies both for noisy synthetic measurements and for artificial data generated by the OLGA simulator.