A self-contained device for the supply of energy to an apparatus (7) driven by gas under pressure, comprises a portable reservoir (1) of cryogenic liquid, and structure associated with the reservoir to withdraw and vaporize liquid from the reservoir and to send it to the apparatus (7). Two circuit portions (2.sub.1, 2.sub.2) incorporate vaporizers (5.sub.1, 5.sub.2) and are delimited between non-return valves (4.sub.1, 4.sub.2) upstream and control valves (6.sub.1, 6.sub.2) downstream. When open, the control valves drive the apparatus (7). The reservoir (1) is of the double wall type (1.sub.1, 1.sub.2), at least one upstream part of the circuit portion (2.sub.1, 2.sub.2) being disposed between these walls (1.sub.1, 1.sub.2). The two circuit portions are in parallel (2.sub.1, 2.sub.2) and the respective valves (6.sub.1, 6.sub.2) are sequentially controlled by a control device (9, 12) which is sensitive to the pressure (P.sub.1, P.sub.2) prevailing in the circuit portions (2.sub.1, 2.sub.2). Preferably, the apparatus (7) is a pump for supplying cryogenic liquid contained in the reservoir (1) to an installation for freezing food stuffs.