Abstract: The present invention provides an improved oxygen filling apparatus adapted to provide oxygen to oxygen cylinders for use in connection with EMS services, ambulances, fire departments, hospitals, veterinary clinics and other services and applications. The present invention includes an oxygen generator unit having at least one molecular sieve, a plurality of pressure sensors, an oxygen sensor, and a PLC control unit with a touch sensitive graphical screen interface configured to selectively display current and historical operational parameters. The oxygen filling apparatus may be adapted for wall mounting and may include a data communications port for remote access, monitoring and troubleshooting.