Methods and apparatus for determining phase fractions (relative concentrations) within a multiphase fluid mixture, in the presence of an injected hydrate inhibitor. Combining this phase fraction information with a hydrate inhibitor injection rate (HIIR) enables resolving oil and water flow rates for the phase fractions. The liquid flow rates and a total combined flow rate of the fluid mixture—determined based on a differential pressure of the fluid mixture through a given area—enable resolving a gas flow rate.