Abstract: Apparatus and methods for the flow analysis of multiphase fluids including a liquid phase in a tubular conduit use Stoneley waves by exciting and detecting sonic wave energy in the tubular conduit. Information about the Stoneley mode component is obtained in one approach by using techniques that excite only the Stoneley mode together with certain other well behaved wave types, and then compensating for the latter. Alternatively the Stoneley arrival is specifically identified in the detected waveforms. Embodiments are described for: determining the flow rate of a liquid; detecting the presence or absence of gas in a liquid; determining the composition by volume of the dispersed phases in a multiphase fluid; determining the size distribution of bubbles in a multiphase fluid; and determining the velocity of slugs in a multiphase fluid.