Abstract Shale gas resources are globally abundant, and the development of these resources can increase CH4 production. It is of interest to study the possibility of enhancing CH4 production by CO2 injection (enhance gas recovery—EGR). Some studies indicate that, in shale, five molecules of CO2 can be stored for every molecule of CH4 produced. The technical feasibility of enhance gas recovery (EGR) needs to be investigated in more detail. The amount of extracted natural gas from shale has increased rapidly over the past decade. A typical shale gas reservoir combines an organic-rich deposition with extremely low matrix permeability. One important parameter in assessing the technical viability of (enhanced) production of shale gas is the sorption capacity. Our focus is on the sorption of CH4 and CO2. Therefore, we have chosen to use the manometric method to measure the excess sorption isotherms of CO2 at 318K and of CH4 at 308, 318 and 336K and at pressures up to 105bar on Belgium dry black shale from a depth of 745m. The shale was obtained from the former coal mine in Zolder in the Campina Basin (North Belgium), which contains Westphalian coal and coal associated sediments of Northwest European origin. We derive the equations for excess sorption in the manometric setup. Only a few measurements have been reported in the literature for high-pressure gas sorption on shales, and interest is largely focused on shales occurring outside Europe. The excess sorption isotherm shows an initial increase to a maximum value of 0.175±0.004mmol/gram for CO2 and then starts to decrease until it becomes zero at 82bar and subsequently the excess sorption becomes negative. Similar behaviour was also observed for other shales and coal reported in the literature. The experiments on CH4 show, as expected, decreasing sorption for increasing temperature. We apply an error analysis based on the Monte Carlo simulation. It shows that the error is increasing with increasing pressure, but that the manometric setup can be used to determine the sorption capacity of CO2 and CH4 on the black shale with sufficient accuracy.