Methods and apparatus are provided for plasma-assisted gas production. In one embodiment, a gas, which includes at least one atomic or molecular species, can flow into a cavity (305). The gas can be subjected to electromagnetic radiation having a frequency less than about 333 GHz (optionally in the presence of a plasma catalyst) such that a plasma (310) forms in the cavity (305). A filter (315) capable of passing the atomic or molecular species, but preventing others from passing, can be in fluid communication with the cavity (305). In this way, the selected species can be extracted and collected, for storage or immediate use.