Between 1999 and 2005, the Gas Technology Institute (GTI), the American Petroleum Institute (API), the United States Minerals Management Service (MMS), and the Pipeline Research Council International (PRCI) co- sponsored an extensive natural gas sampling research program at the Metering Research Facility (MRF), located at Southwest Research Institute (SwRI). The results of this research provided a basis for the most recent revisions to the API Manual of Petroleum Measurement Standards (MPMS) Chapter 14.1, Collecting and Handling of Natural Gas Samples for Custody Transfer. The research supported revisions that produced both the 5th edition of the standard, published in 2001, and the 6th edition, published in February 2006.