The American Gas Association has published (June, 1998) a recommended practice; Report No. 9; Measurement of Gas by Multipath Ultrasonic Meters. This paper reviews some of the key contents of A.G.A.-9 including recommended meter performance requirements, design features, testing procedures, and installation criteria. An update for the committee work in progress for year 2001 and beyond is integrally included. The paper addresses some of the most commonly asked questions by new users of the document. A.G.A.-9 was drafted by the A.G.A. Transmission Measurement Committee (TMC) which incorporated many of the recommendations in the GERG Technical Monograph 8 (1995) and certain related OIML recommendations. After two years of technical discussions, balloting, and revisions, the document represents the consensus of several dozen metering experts in the US and Canada. They represent a crosssection of senior measurement personnel in the natural gas industry. The ISO/TC 30 standard currently being written for ultrasonic meters has mostly adapted A.G.A.-9 information and is adding various additional pieces of operating practice information, precautions and recommendations. A much larger data base now exists for performance and calibration history of USMs, including additional test data for piping, flow conditioners and valve interaction