NOVELTY - Apparatus for determining concentrations of components in a gas mixture (2) flowing through a pipeline (1), comprises: an ultrasonic flow measuring device, which determines the sound velocity of the gas mixture flowing in a pipeline; a temperature measurement unit, which determines the temperature of the gas mixture flowing in the pipeline; and an evaluation unit, which determines the concentrations of the components of the gas mixture, based on sound velocity determined by an ultrasonic measurement, and based on sound velocity which is obtained by evaluating the ideal gas equation.    USE - The apparatus is useful in process- and automation technology.    ADVANTAGE - The apparatus ensures precise determination of the concentrations of components in a gas mixture, and improved coupling and decoupling of the ultrasonic measuring signals into the gas mixture.    DETAILED DESCRIPTION - Apparatus for determining concentrations of components in a gas mixture (2) flowing through a pipeline (1), comprises: an ultrasonic flow measuring device, which determines the sound velocity of the gas mixture flowing in a pipeline; a temperature measurement unit, which determines the temperature of the gas mixture flowing in the pipeline; and an evaluation unit, which determines the concentrations of the components of the gas mixture, based on sound velocity determined by an sonic flow measuring device, and based on sound velocity which is obtained by evaluating the ideal gas equation, where the gas mixture is a biogas and comprises three essential components comprising methane, carbon dioxide and water vapor. The evaluation unit determines the concentration of water vapor depending on the temperature and the humidity of the gas mixture, and the concentration of water vapor is considered during determining the concentrations of the other two components    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic longitudinal section of the ultrasonic flow measuring device.    Pipeline (1)    Gas mixture (2)    Mounting stud (3)    Ultrasonic sensor with temperature sensor (4)    Transducer (5)