Source: US. Bureau of Labor Statistics
Release: Consumer Price Index
The term "utility (piped) gas service" refers to natural gas.
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://fred.stlouisfed.org/series/CUUR0000SEHF02, December 4, 2016.