A sealing apparatus and related method for sealing an annular space between concentrically disposed members. In an exemplary embodiment, the method includes providing a sealing ring within the annular space, the sealing ring defining oppositely inclined interior and exterior surfaces each having a generally frusto-conical shape and defining opposing first and second edges, a nose adjoining the respective first edges of the interior and exterior surfaces, and a first convex surface adjoining the respective second edges of the interior and exterior surfaces opposite the nose; and forming a seal against a fluid pressure in the annular space, comprising depressing the first convex surface of the sealing ring so that the interior and exterior surfaces thereof expand radially to exert contact stress on each of the concentrically disposed members.