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 [CUUR0000SEHF02], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/CUUR0000SEHF02/, September 3, 2015.