Abstract: A method and apparatus for the measurement of the properties of fuel gases dependent upon flow and pressure, and more particularly upon the dyanmic viscosity and/or the density of the fuel gases. The apparatus includes a device to control the flow of the fuel gas and at least one flow restrictor in the gasway. The design and the operation of such an apparatus is simplified by the integration of a gas holding device having a capacity which changes in response to the pressure difference between the pressure inside the inner chamber of the device and the ambient pressure. An aneroid capsule element in a line connecting a closeable gas inlet and at least one flow restrictor may be used for this purpose. A time measurement device may be switched on and off as a function of predetermined capacities of the gas holding device.