One can transport and store oxygen more efficiently (volume and weight of tank) if it is liquid under the order of 1 atmosphere. Liquid oxygen (LOX) is kept cryogenic in insulated tanks for short periods of time as a propellant in rockets, and for weeks just about anywhere in well insulated but heavier tanks (see below). I believe oxygen is transported from earth to the ISS as LOX, as suggested in this question.
On the ISS is there a (at least some) supply of oxygen that is stored as LOX? Is the "cold of space" when the sun isn't shining ever used to keep it cold, or just good insulation and a refrigerator? Writing this answer got me thinking about this. LOX boils at about 54K at 1 atmosphere. If heat leaks into the tank through insulation or the liquid access connection or boil-off vent, it is removed by the boil-off process. However if you need to make it last a long time, supplemental cooling might be necessary.