This release presents provisional volcanic gas monitoring data from multi-GAS (multiple Gas Analyzer System) station "YELL_MUD", installed in July 2021 in the Obsidian Pool thermal area, Yellowstone National Park, USA. The multi-GAS station includes gas sensors to measure water vapor, carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen sulfide (H2S) in gas plumes, as well as meteorologic parameters (wind speed and direction, ambient temperature and relative humidity, ambient pressure), and the temperature of a nearby geothermal feature. The station is duty cycled to conserve power and collects data for 30 minutes every 6 hours beginning at 00:00, 06:00, 12:00, and 18:00 UTC. Before each measurement cycle the gas sensors' baseline responses are checked by recirculating trapped air through chemical scrubbers (soda lime and anhydrite) to remove acid gases and water vapor. On-site CO2, SO2, and H2S standard gases are sampled every 28.25 days to verify the sensor responses. High-rate data are logged onsite and half-hourly averaged values from each sample cycle, along with baseline ('zero') and verification ('span') results, are telemetered every 6 hours by a BGAN satellite system. The half-hourly averages and diagnostic data obtained via telemetry are presented herein. Real-time values from the station can be viewed on the USGS Yellowstone monitoring webpage by clicking on the small 'gas cloud' icon (https://www.usgs.gov/volcanoes/yellowstone). Please note that the data presented herein are provisional, as described below. For a more detailed technical description of the multi-GAS instrument please see Lewicki et al., 2017. PROVISIONAL DATA DISCLAIMER: These data are preliminary or provisional and are subject to revision. They are being provided to meet the need for timely best science. The data have not received final approval by the U.S. Geological Survey (USGS) and are provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the data. While every effort is made to obtain accurate measurements, volcanic environments can be extremely harsh and provisional data and results generated by automated processing routines have not been analyst-reviewed and may be inaccurate due to instrument malfunctions, sensor drift, or other problems. Any such problems may take some time to address due to the remote location of the site. Users are cautioned to carefully consider the provisional nature of the data before using it. Information concerning the accuracy and appropriate uses of these data may be obtained from the USGS. Reference Lewicki, J.L., Kelly, P.J., Bergfeld, D., Vaughan, R.G., Lowenstern, J.B., 2017. Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach. J. Volcanol. Geotherm. Res. 347, 312–326. https://doi.org/10.1016/J.JVOLGEORES.2017.10.001