Abstract: A wellhead assembly in which an in-line tree (10) is landed within a wellhead housing (3). The in-line tree has a vertical production through bore (11), two hydraulically or electrically controllably in-line valves (13A, 13B) in the vertical production bore, and a lateral bore (16) leading from the vertical production through bore. A horizontal tree (20) having a vertical through bore (23) is landed on the wellhead housing (3) so that the in-line tree (20) is within the vertical bore. The horizontal tree has a lateral bore (24) which is aligned with the lateral bore (16) of the in-line tree. The in-line tree (10) can be run in and retrieved through the horizonal tree (20). Alternatively the horizontal tree (20) can be removed from the wellhead housing (3) without a BOP if the in-line valves (13A, 13B) are closed.