Abstract: A seal of annular configuration sealingly engaged with an annular surface of an element, to inhibit a communication thereacross of low- and high-pressure environments of the surface, and either one, or a pair of annular support rings engaging the seal. The seal and rings have interfacing and tapered or inclined surfaces and, consequently, the seal is restrained against (a) an unwarranted movement toward the surface being sealed, thereby to prevent its unwarranted extrusion, and (b) heavy radial gas force in that the gas forces act axially and radially on the support rings.