J.V. Vogel assumed multiphase flow occurs in these structures to derive an empirical equation used to construct their IPR curves. These structures are controlled by assemblies that are named for their loose resemblance to Christmas trees. Light interventions (10[1])perform maintenance on these structures using slickline, braided wireline, or coiled tubing without interrupting operations. (10[1])The (-5[1])line of spontaneous potential measurements from these structures (10[1])deflects left or right based on the relative salinity of the mud filtrate and formation water. The practice of logging these structures developed out of the Schlumberger (“shlum-bur-zhay”) brothers’ attempts at finding iron ore using electrical resistivity measurements. The productivity index of these structures has units of bbl per day per (10[1])psi (10[4])(“P-S-I”). When (-5[1])pressure safety systems fail in these structures, (10[1])blowouts (-5[1])occur. (10[1]-5[3])For 10 points, (-5[2])name these structures (-5[1])drilled by rigs (10[2])to extract (10[1])hydrocarbons. (10[4])■END■ (10[7])