A method and system for determining a flow rate of at least a phase or a component of a fluid produced from an oil and gas well are presented hereinafter. The fluid is one of a multiphase and of a multicomponent fluid. The method comprises, in a training phase, collecting primary measurements of pressure, temperature, and additional flow parameter of the produced fluid. The primary measurements are carried out at the wellhead by a set of sensors installed in a flow line for the produced fluid. In the training phase, the method also comprises collecting a flow rate of at least one of the phases or components of the produced fluid simultaneously measured by a reference multiphase flow meter installed in the flow line. It also includes establishing a relationship between the pressure, temperature, and the additional flow parameter and the flow rate of the at least one of the phases or components of the produced fluid. The method also comprises, in a subsequent production phase, determining the flow rate of the at least one of the phases or components of the produced fluid based on the primary measurements of the pressure, temperature, and the at least one additional flow parameter and on the established relationship.