This paper describes the current contents of the United States (U.S.) orifice flow metering standard − American Petroleum Institute (API) Manual of Petroleum Measurement Standards (MPMS) Chapter 14.3, “Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids,” Part 2, “Specification and Installation Requirements.”[1] This document is also known as American Gas Association Report No. 3, Part 2.[2] As of the writing of this paper (i.e., June 2016), this standard was in its fifth edition and was last revised in March 2016.