for gathering data such as pressure, temperature, sand flow, erosion, multiphase flow, and single phase flow such as water or gas. Surface and subsea Christmas tree images See also References API Specifications 6A and 17D. GE Oil & Gas XT ISO 10423:2009 Petroleum and natural gas industries - Drilling and production equipment - Wellhead and Christmas tree equipment NORSOK STANDARD D-010, Well integrity in drilling and well operations, Rev. 3, August 2004 Oil wells Petroleum production