This paper described the current contents of the United States orifice flow metering standard – American Petroleum Institute (API) Manual of Petroleum Measurement Standards (MPMS) Chaper 14.3, “Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids”, Part 2, “Specification and Installation Requirements.”(1) This document is also knows as American Gas Association Report No. 3, Part 2 (2). As of the writing of this paper (i.e. May 2015), this standard was in its fourth edition, second printing. It was last revised in April 2000 and is in the process of being revised again. The revised document is currently in the ballot process at API and it is anticipated that the new version likely will be published by the end of 2015.