Abstract: A container for holding a cryogenic, two constituent liquid, is described. The container has two vent conduits disposed at different altitudes or levels inside the container wherein a first, cryogenic liquid is filled into the container until it vents from the first conduit. Then, a second, cryogenic liquid is filled into the container until the combined liquids vent through the second conduit. The vent conduits are preferably positioned to provide intended percentages of the various constituents comprising the liquid.