NOVELTY - Apparatus comprises: a pressure chamber; and a gas-producing microorganism within the chamber, where the pressure chamber is capable of maintaining a gas pressure of at least 0.5 psi above atmospheric pressure.    USE - The apparatus is useful for repeatedly generating gas pressure from microorganisms (claimed) and in autonomous sensors, unmanned underwater vehicles and portable power supplies, where the gas includes hydrogen, carbon dioxide and gaseous fuels including hydrocarbons, methane, ethane and propane.    ADVANTAGE - The apparatus regenerates the gas pressure by utilizing gas-producing microorganisms and thus: eliminates the need to transport tanks to external fueling stations; generates gaseous fuels on-site using biomass; and provides ballast for long-duration aquatic sensors, communication relays and buoys.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a method (I) for repeatedly generating gas pressure, comprising: providing the apparatus in which a food source for the microorganism is within the pressure chamber; and allowing the gas pressure in the pressure chamber to increase to at least 0.5 psi above atmospheric pressure;    (2) a method (II) for repeatedly generating gas pressure, comprising: (a) submerging the apparatus in a liquid, where a food source for the microorganism is within the pressure chamber; (b) allowing the gas pressure in the pressure chamber to increase to at least 0.5 psi above atmospheric pressure; (c) venting a portion of the gas through the vent and into the dry chamber; and (d) moving a portion the gas in the dry chamber through the gas valve and into the ballast chamber, so that a portion of the liquid in the ballast chamber moves to the exterior of the container and the container rises;    (3) a method (III) for repeatedly generating gas pressure, comprising: steps (a) and (b) as above per se; venting a portion of the gas through the vent and into the floater chamber; allowing the floater chamber to pivot until a portion of the gas escapes from the floater chamber through the second gas vent; and allowing the floater chamber to return to a position at which gas does not escape from the floater chamber; and    (4) a method (IV) for repeatedly generating gas pressure, comprising: submerging the apparatus in the liquid; allowing the gas pressure in the pressure chamber to increase to 0.5 psi above atmospheric pressure; and venting a portion of the gas through the vent and into the bladder.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the a pressure chamber of the apparatus.