A new reactor concept has been developed and tested for the conversion of methane into ethane, ethylene and higher hydrocarbons via oxidative coupling. The basic idea consists of providing a low oxygen concentration in the reactor in order to increase hydrocarbon selectivity. To this end, oxygen is supplied to the reacting mixture by permeation through a porous wall, which is capable to withstand the temperatures and pressures involved, and at the same time give adequate values of oxygen flux. In this part, the main requirements of this type of reactor are discussed, as well as some operational constraints. The modifications carried out on the starting ceramic membranes are described and their properties are characterized at different stages of the process.