A system for determining densities and proportions of phases in a multi-phase fluid flow (MFF) that can include an oil phase, a water phase, and a gas phase from a well. The system includes a first density sensor that senses the MFF at locations where the phases of the MFF are often separated, a second density sensor senses the MFF from the output of a phase mixer-homogenizer, and a third density sensor that senses, in real time, the MFF where the gas phase starts to separate or has separated from the liquid phase but where the liquid phases have not separated. The system also includes one or more processors for executing one or more programs to determine a density of the oil phase, a density of the water phase, a density of the gas phase, and proportions of phases including a water cut and a gas volume fraction based on readings from the first, second, and third density sensors.