Oxygen is a light blue gas transportable via pipes. Canisters of oxygen can be purchased from traders or salvaged by logistics drones.
Oxygen is a life requirement for the population. The atmosphere must be rich in oxygen and poor in CO2 for long term survival.
Oxygen is added to the atmosphere by an airduct supplied with an both power and a pipe connected to an oxygen supply. Oxygen can be added to pipes using loaders, created using an oxygen maker, reprocessed with an air processor and CO2 scrubber, or supplied via an existing tank.