This publication contains routine analyses and related source data for 475 natural gas samples from 17 states and two foreign countries. Of this total, 454 samples were collected during calendar year 1971. The remaining 21 samples were collected during previous years, but releases granting permission to publish the analyses were not received until 1971. All samples were collected as part of a continuous survey of the free world for occurrences of helium in natural gas. This survey has been conducted in the United States by the Bureau of Mines since 1917. In late 1965, the survey was expanded to include foreign gasfields. The analyses published here were made by mass spectrometer and a special helium analyses apparatus, which are described in Bureau of Mines bulletins 486 and 576. Thirteen previous publications have presented the results of 9,427 gas analyses prior to 1971. The first three, bulletins 486, 576, and 617, contain analyses and related source data on 5,218 gas samples collected from 1917 through 1960. The other 10 publications, which were issued as information circulars, supplement the three bulletins and contain 4,209 analyses of samples collected since 1960. This publication is the 11th publication supplementing the three bulletins.