A method of determining the dryness of a multiphase fluid flow, such as a steam flow, in a fluid line, the method comprising: determining a value of a flow velocity parameter which is a function of the flow velocity of the fluid flow in the fluid line using a flow sensor; 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; characterized by: analysing the vibration signal to determine a value of an energy parameter which is related to an amplitude of the vibration signal within a frequency band; and determining a dryness parameter relating to the dryness of the multiphase fluid flow in dependence on the values of the flow velocity parameter and the energy parameter, based oh a pre-determined correlation of the flow velocity parameter and the energy parameter with the dryness parameter; wherein determining a dryness parameter comprises accessing a database containing data correlating flow velocity parameters and energy parameters with dryness parameters; wherein the energy parameter is selected from the group consisting of: an amplitude of a resonant frequency of the vibration signal; a total energy of the vibration signal determined by summing the amplitudes of all frequencies within the frequency band; an amplitude of the peak frequency within the frequency band; and an average amplitude of all frequencies within the frequency band. determining a value of a flow velocity parameter which is a function of the flow velocity of the fluid flow in the fluid line using a flow sensor; 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; characterized by: analysing the vibration signal to determine a value of an energy parameter which is related to an amplitude of the vibration signal within a frequency band; and determining a dryness parameter relating to the dryness of the multiphase fluid flow in dependence on the values of the flow velocity parameter and the energy parameter, based oh a pre-determined correlation of the flow velocity parameter and the energy parameter with the dryness parameter; wherein determining a dryness parameter comprises accessing a database containing data correlating flow velocity parameters and energy parameters with dryness parameters; wherein the energy parameter is selected from the group consisting of: an amplitude of a resonant frequency of the vibration signal; a total energy of the vibration signal determined by summing the amplitudes of all frequencies within the frequency band; an amplitude of the peak frequency within the frequency band; and an average amplitude of all frequencies within the frequency band. analysing the vibration signal to determine a value of an energy parameter which is related to an amplitude of the vibration signal within a frequency band; and determining a dryness parameter relating to the dryness of the multiphase fluid flow in dependence on the values of the flow velocity parameter and the energy parameter, based oh a pre-determined correlation of the flow velocity parameter and the energy parameter with the dryness parameter; wherein determining a dryness parameter comprises accessing a database containing data correlating flow velocity parameters and energy parameters with dryness parameters; wherein the energy parameter is selected from the group consisting of: an amplitude of a resonant frequency of the vibration signal; a total energy of the vibration signal determined by summing the amplitudes of all frequencies within the frequency band; an amplitude of the peak frequency within the frequency band; and an average amplitude of all frequencies within the frequency band. an amplitude of a resonant frequency of the vibration signal; a total energy of the vibration signal determined by summing the amplitudes of all frequencies within the frequency band; an amplitude of the peak frequency within the frequency band; and an average amplitude of all frequencies within the frequency band.