A modular oxygen supply system is provided comprising at least one module skeleton with a baseplate with frames arranged in parallel to one another. The system includes supply lines for ambient air with air connections for taking off the air, first gas lines for oxygen with first gas connections for taking up the oxygen and second gas lines for outgoing air with second gas connections for taking up outgoing air. Rack guides with data lines are provided. At least one individual module can be pushed into the module skeleton. Each individual module has at least one molecular sieve container fastened on a baseplate with the gas connections and with an electric contact. Each individual module has a gas treatment unit for the ambient air fed in. A pressure reducer and a multiple-way valve as well as an oxygen reservoir are arranged downstream of the molecular sieve container or containers connected in parallel. Each individual module is pushed into the module skeleton and is connected via the gas connections to a supply line for the ambient air, to a first gas line for oxygen and to a second gas line for the outgoing air. The electric contact of the individual module is connected to the data line of the module skeleton.