Abstract: A method and apparatus utilizing inelastic neutron scattering for measuring the volume fractions of the various constituents of a multiconstituent substance. A source of fast neutrons is positioned proximate the substance. A detection system is provided to monitor the gamma emissions resulting from inelastic scattering of the fast neutrons from the various nuclides within the substance. The resulting measurement of the relative abundance of gamma emissions characteristic of the various nuclides within the substance is used to determine the relative concentrations of the major constituents of the substance. In a preferred embodiment, the present invention is used to provide a real-time measurement of the volume fractions of oil, gas and water in the production flowstream from an oil well.