Wellhead christmas tree is an assembly of valves, spools, and fittings used for an oil well, gas well, water injection well, water disposal well, gas injection well, condensate well and other types of wells. It was named for its crude resemblance to a decorated tree.

The Oilfield Wellhead christmas tree is an assembly of valves, spools and fittings for an oil well, and to design to direct and control formation fluids from the well. It can provide inlet for production tubing strings, including all components above the tubing head adapter. Wellhead christmas tree assemblies can constitute many different kinds of combinations in order to meet any special requirement. Based on their different functions, Wellhead christmas tree can be classified into such special Wellhead christmas tree as oil production (flowing and artificial lift) Wellhead christmas tree, gas (natural gas and various sour gas) production Wellhead christmas tree, water injection Christmas trees, thermal recovery Christmas trees, fracturing Wellhead christmas trees and acidizing Christmas trees. Different pressure ratings serialize Wellhead christmas trees.

The gas production Wellhead christmas tree and tubing head are mainly used to produce gas and inject gas. The relative density of natural gas is low and gas column pressure is low, while well head pressure is high and liable to leakage regardless of gas production and gas injection. Sometimes natural gas contains corrosive media such as H2S and CO2. Therefore, the gas production Christmas tree calls for rigid requirements on both its materials and its sealing characteristics. For the sake of safety, two gate valves are used on the tubing and casing respectively. Some gate valves to be used on high pressure and ultra-high pressure gas wells are integrated valves manufactured from high quality forged steel.