An improved wellhead structure including a wellhead housing having a sealing surface with grooves therein and pressure compensating material in the grooves, a sealing sleeve having inner and outer resilient seal rings and an internal actuating groove with upper and lower shoulders, an actuating ring having an outer flange engaged within the internal groove in the sleeve and an external surface tapering downward and inwardly and a hanger with an upstanding rim having external grooves with pressure compensating material in the grooves and having an inner surface which tapers upwardly and outwardly and is engaged by the external tapered surface of the actuating ring and upper and lower external seals and a port extending from the interior of the actuating ring to its exterior into the area between such seals so that pressure applied through the port forges the hanger rim and the sealing sleeve outward to ensure positive metal-to-metal sealing across the annulus between the exterior of the hanger rim and the interior of the wellhead housing.