Abstract: A hydraulically controlled ram assembly 12 for an oilwell blowout preventer 10 effects the opening and closing of a ram block 30 interconnected with a piston 34. The piston 34 is movable within the ram housing 22 in response to a hydraulic pressure to seal the ram block 30 with an oilfield tubular. The hollow ram shaft 36 having a central bore is sealed with a door 20 pivotally mounted to the BOP body 16 by one or more ram shaft seals 52. The cylindrical bore 60 in the ram shaft 36 is in fluid communication with the central passageway 18 in the BOP body. A ram shaft rod 70 secured to a ram housing end plate 40 extends radially inward into the bore 60 in the ram shaft 36, and is sealed to the ram shaft by one or more rod seals 72. Wellbore pressure within the BOP that opposes ram closing is thus reduced by the sealing area of the rod seal relative to the sealing area of the ram shaft seal.