This paper described the current contents of the United States 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 [ 1] 2, “Specification and Installation Requirements.” This document is also known as American Gas Association Report No. 3, Part 2.[2] As of the writing of this paper (i.e., May 2014), 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 will be published by the end of 2014.