A method and apparatus for determining the flow rates of a multi-component fluid mixture is disclosed. The temperature and pressure of the multi-component mixture is determined. The fractions of the multi-component mixture are determined based on at least two measured physical properties of the mixture and knowledge of the same physical property of the individual components. The velocity of the multi component mixture is determined. The flow rate of the individual component of the fluid is determined. An electromagnetic measurement is performed. A statistical parameter related to the electromagnetic measurement is calculated and compared to an empirical derived threshold value corresponding to the value of the statistical parameter when only one of the components of the multi component mixture is present. The thickness of unwanted deposits on the pipe wall is determined and an improved flow rate determination of the individual components of the fluid is obtained.