The term "utility (piped) gas service" refers to natural gas.
Source: US. Bureau of Labor Statistics
Release: Consumer Price Index
US. Bureau of Labor Statistics, Consumer Price Index - All Urban Consumers - Utility (piped) gas service [CUSR0000SEHF02], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/CUSR0000SEHF02/, June 2, 2015.