Methane is the major final product of anaerobic degradation of biomass in. Moreover, methane has a high greenhouse gas potential. Therefore it is important to gain a comprehensive picture of the methane cycle, while also knowing the methane flux from the sediment into the water column and further into the atmosphere. In order to determine the exact concentrations of methane in the boundary layer between the sediment and the water column, a diffusion based methane-sensor, , is presented in this work. The sensor consists of a steel cannula with two small holes at the tip, which are coated with a gas-permeable silicone tubing. Methane can therefore diffuse into the interior of the needle. With the help of a carrier liquid (distilled water), the methane sample is pumped to the gas chromatograph. Because of the GC can only register gases, the methane must be removed from the distilled water. This is done, by using a degassing chamber. The carrier liquid is pumped through a gas-permeable silicone tubing, so the methane diffuses into a carrier gas stream. The gas stream including the methane sample is then directed to the GC detector, where the methane is analyzed. The methane, which diffuses from the sediment into the needle, is pumped into some sort of coil to be stored until measurment in the laboratory. Several coils were tested for their methane permeability.. In a next step, several methane samples are pumped in a row into the coil. In order to minimize mixing of the individual samples, several "stop liquids" with a lower solubility, than water, were pumped between the samples. Best performance was obtained with a steel coil and no stop liquid. However, the reproducibility of the system was low and severe losses of methane were observed. Thus the tested system is no option for storage of methane samples.