The molecular beam epitaxy (MBE) process is generally surrounded by liquid nitrogen (LN2) cooled surfaces for optimum control of the environment in which the thin-film deposition takes place. The design and operation of a LN2 supply system for feeding the cryogenicly cooled surfaces in a MBE system is described here. The supply system is based on modification of a standard 50-l LN2 storage dewar. The reservoir gravity feeds liquid through a vacuum-insulated line into the fill port of the MBE system. A solenoid-operated vent valve activated by a temperature controller regulates the level of LN2 in the MBE system. The LN2 SUPPlY system is efficient and costs much less than other alternatives.