An oxygen cylinder holds more gas if filled first with a sponge-like powder. Jared DeCoste of Leidos, Inc. in Maryland and colleagues searched among 10,000 metal-organic frameworks using a Monte Carlo simulation, and found two that increase the capacity of an empty cylinder by 89% and 114% at a pressure of 140 bar. This should allow for smaller, lighter oxygen tanks that require lower pressures, and has implications for divers, fighter pilots, astronauts, and anyone who needs medical oxygen.