Abstract: A hydraulic system and method are provided for supplying high pressure hydraulic fluid to a cylinder for operating a ram, e.g. a shearing and/or shut-off ram for a blowout preventer. It comprises means for supplying high pressure hydraulic fluid to the cylinder, said hydraulic fluid supply means comprising first and second storage means for storing hydraulic fluid under pressure, first conduit means for supplying hydraulic fluid under pressure from said first storage means to the cylinder, a pressure sensing device for determining the back pressure in said first conduit means, second conduit means for supplying hydraulic fluid under pressure from said second storage means to the cylinder and valve means for automatically opening said second conduit means when the back pressure in the first conduit means reaches a predetermined amount.