Abstract: Multiphase flows are common in the petroleum industry, and yet their measurement always nearly presents difficulties to the process engineer. The traditional solution to the problem of metering multiphase flows is to separate the components of the flow first, and then measure the flow rate of each using conventional single-phase instruments, such as turbine meters and orifice plates. The problem of how to meter oil-gas-water mixtures has been of interest to the petroleum industry since the early 1980s. Since then considerable research has been conducted into the development of a three-phase flow meter suitable for the use in an industrial environment. This paper discusses why three-phase flow measurement is important, and why it has proved such a difficult problem to solve. Some of the principal technologies and strategies which have been developed over the last decade for oil-gas-water three-phase flow measurement are described. Fi- nally, future developments in this area are considered.