Over the past ten years, the Gas Technology Institute (GTI), the American Petroleum Institute (API) and the United States Minerals Management Service (MMS), have co-sponsored an extensive natural gas sampling methods research program at the GTI Metering Research Facility (MRF), located at Southwest Research Institute (SwRI). The results of this research provided a basis for the revision of Chapter 14.1 (i.e., Collecting and Handling of Natural Gas Samples for Custody Transfer) of the API Manual of Petroleum Measurement Standards (MPMS). The last revision was published in 2001, and work is beginning in 2005 on a new edition that will incorporate the latest research findings. The API Chapter 14.1 Working Group, a research steering committee consisting of natural gas sampling experts from major oil and gas companies, provided input that helped focus the project on improving current field practices. The research identified several causes of natural gas sample distortion, as well as techniques for avoiding gas sample distortion. The research data illustrated how errors in calculated gas properties, such as heating value and density, can occur as a result of poor sampling technique