Abstract: A buried fluid storage tank with a single fluid-tight enclosure which comprises an external concrete enclosure buried into the ground, a rigid structure with a bottom slab and possibly a covering dome as well as a fluid-tight heat-insulating envelope which defines inside of the structure a fluid loading space, whereas the external enclosure has the shape of a thick substantially fluid-tight wall, this enclosure as well as the covering dome being made integral with each other from one single piece of material and forming together with the bottom slab the stiffening structure of the tank, the invention being applicable to a confinement tank in particular for a harbor terminal for loading a liquefied natural gas.