In the complete KTB-VB and in in the KTB-HB down to a depth of 3003 m the gas phase was released and collected by twirl degassers attached in front of the mud shakers. This open system led to gas losses as well as air contamination. Therefore results obtained down to this depth have only qualitative character. After casing the KTB-HB to a depth of 3003 m a bypass system was installed at the BOP (blow-out preventer) 50 cm below the flow line. A constant part (about 100 l/min) of gas-bearing drill mud is pumped through the bypass directly to a twirl degasser which is isolated against atmosphere. To prevent air contamination or sucking off drill mud the pressure in the gas trap is balanced by charging argon. The released gas phase is completely sucked off and led through a heated hose (in order to prevent water condensation or freezing) to the logging unit and there parallel to the measuring systems gaschromatograph, mass spectrometer and radon logging device.