British expeditions all used open-circuit oxygen apparatus, as advocated by pioneer climbers George Finch, Noel Odell and Peter Lloyd. Open-circuit oxygen apparatus was trialled on the 1922 and 1924 British Everest expeditions; the bottled oxygen taken by the 1921 expedition was not used. The carrying frame used in 1922 and 1924 with four cylinders of oxygen or gas weighed a hefty 32 lb (14.5 kg), though climbers sometimes (e.g. the last climb of Mallory and Irvine) carried only two cylinders each. Four cylinders contained a total of 960 litres of oxygen, which would last for eight hours at the standard rate of 2 litres per minute or seven hours at 2.2 L/min.