The usual inflation system is through a low-pressure hose from the primary breathing gas supply, but a dedicated direct feed pony bottle was common on early buoyancy compensators, and remains an option for some models. Most BCs allow oral inflation both underwater and on the surface. This could theoretically reduce gas consumption, but is generally not considered worth the effort and slightly increased hazard of taking the DV out of the mouth underwater, and possibly having to purge it before breathing again. Oral inflation is, however, an effective alternative inflation method in case of a failure of the pressurized inflation system. Emergency inflation by expendable CO2 cartridge is provided on some BCs.