A pressure vessel for receiving at least one fluid medium has a first shell (1) and a second shell (3) at least partially encompassing the first shell (1). The first shell (1) has, at least at one of its ends, a collar portion (5) having a securing element (15) that forms an opening (13) for supplying and discharging the medium. A support element (19) in the form of a split ring surrounds the opening (13), is provided inside the container and has a contact surface (39) adapted to the curved shape of the first shell (1) inner side attached to the collar portion (5). The contact surface is able to be pressed onto the first shell inner side attached to the collar portion (5). The contact surface is able to be pressed onto the first shell (1) using a pressing device (43, 45).