A method of determining the phase compositions of a multiphase fluid flow in a fluid line, including obtaining a vibration signal from the fluid flow using a vibration sensor comprising a target disposed in the fluid flow which vibrates in response to fluid flow in the fluid line. The vibration signal is analyzed to determine a first energy parameter which is related to the energy of the vibration signal within a first frequency band, and a second energy parameter which is related to the energy of the vibration signal within a second frequency band; and a phase composition parameter, such as a dryness parameter, relating to the phase compositions of the fluid flow is determined using the first and second energy parameters. An apparatus for determining the phase compositions of a multiphase fluid flow in a fluid line.