A Christmas tree is a piece of equipment that provides flow control on a oil or gas well. Christmas trees are a vertical assembly of valves with gauges and chokes that allow for adjustments in flow control as well as injections to stimulate production. Christmas trees are so-called because the collection of components can resemble a Christmas tree if you have the right amount of imagination. The valves that comprise some of the decorations on the Christmas tree are opened when the oil or gas well is ready to produce and the processing and storage facilities are ready to receive. The other decorations are devices that facilitate pressure relief, monitoring and chemical injection.