The amount of oxygen generated in a SF6 dense plasma by the etching of the quartz tube walls surrounding the plasma source of the helicon reactor has been measured. Two complementary techniques have been used to identify the wall etch products and the measurement of their equivalent flux : plasma induced emission spectroscopy of oxygen atoms (actinometry) and mass spectrometry by comparison with the amount of the isotopic oxygen (O-18(2)) introduced into the plasma. It appears that, with a 5 mm air gap between the antenna and quartz walls of the reactor, the equivalent oxygen outgassing flux ranges from 2 to 4 seem, depending on the SF6 pressure and the radio frequency power applied. This corresponds to an oxygen concentration in the gas phase between 15% and 40%, depending on the operating conditions. This result should be considered for the development of future dense plasma reactors using quartz walls and for improvement of the performance of the present generation of inductively coupled and electron cyclotron resonance plasma reactors.