The American Gas Association published Report No. 9, Measurement of Gas by Multipath Ultrasonic Meters [Ref 1] in June 1998. It is a recommended practice for using ultrasonic meters (USMs) in fiscal (custody) measurement applications. This paper reviews some of history behind the development of AGA Report No. 9 (often referred to as AGA 9), key contents and includes information on meter performance requirements, design features, testing procedures, and installation criteria. This paper also discusses changes that will be incorporated in the next revision. At the time of this paper the expected publication date is the Fall of 2006