A new system has been developed to determine absolute quantities of gas (mainly noble gases) released during thermal desorption in the range from 10-12 to 10-5 moles with a precision of few %. The system is actually designed for simultaneous measurement of gaseous elements like He, Xe, Kr, thermally released from nuclear fuel samples and also allows the determination of the release kinetics as a function of time. This system called Quantitative GAs MEasurement System (Q-GAMES) is based on the principle of collecting, purifying and spiking the sample gas in a "high pressure" chamber, and continuous sampling of the gas for mass spectrometric analysis without sample depletion during the experiment. It is equipped with its own spike generator and with different gas purification systems. It is shown that this system fulfils the requirement to work with two existing very high temperature gas desorption facilities for nuclear materials. This paper describes the Q-GAMES principle, the spiking system, its calibration, its operative mode, the different quantification techniques, as well as its technical data, in combination with some examples of typical application.