In oil and gas production, the valve assembly installed on a producing wellhead is called a Christmas tree.
A Christmas tree is a group of valves, spools, pressure gauges, and chokes fitted at the top of an oil or gas well. It controls production, regulates pressure and flow, and provides access for well-servicing operations. The assembly is installed after drilling and completion have prepared the well for production.
The name refers to the branching appearance of the valves and connected equipment, not to a seasonal function. A Christmas tree should not be confused with a blowout preventer. A blowout preventer is primarily drilling safety equipment used to control an unexpected influx of formation fluids, while the Christmas tree is normally associated with a completed production well.
Subsea wells also use Christmas trees, although their designs are adapted for installation and operation on the seafloor. Surface and subsea versions can include remotely operated valves and monitoring systems.