Emission Trends Associated with Natural Gas Liquids Supply

 For suppliers of natural gas liquids, the CO2 associated with natural gas liquids (NGLs) supplied to the U.S. economy (i.e., ethane, propane, butane, isobutane and pentanes plus) has gradually increased from 212 million metric tons (MMT) in 2011 to 434 MMT in 2020. Except for a small decrease in 2013, the supply of NGLs has increased steadily every year with ethane and propane making up about 70 percent by volume of the NGLs supplied each year by U.S. fractionators. [1]

The increase in NGL supply is due to increased production of natural gas in areas that are high in natural gas liquids; increased U.S. demand for NGL products; increased production capacity due to construction of new fractionation plants (124 plants in 2020 compared with 116 in 2011); and increased production at existing plants (ratio of CO2 to number of plants increased from 2.6 MMTCO2/plant in 2017 to 3.5 MMTCO2 /plant in 2020); The year-over-year increases in the CO2 emissions from NGLs were approximately 12 percent for 2018 and 2019, and 8 percent for 2020. The increased NGL production reported in recent years is also partly due to increased exports due to the construction of new pipelines and export terminals. [2] Exports of propane have increased every year since 2012 due to strong market demand in Asia.[3] Ethane supply increased in 2019 in response to increased demand from new petrochemical facilities in the U.S. that use ethane as a feedstock. [4]

The reported CO2 for 2011 and 2012 are also affected by changes in the default emission factors. For suppliers of natural gas liquids, the default emission factors used for calculating the CO2 for ethane, propane, butane and isobutene were revised in 2013. The default emission factors for propane, butane and isobutane were increased by a few percent over those used prior to 2013, while the default emission factor for ethane was decreased by over 30 percent. The impact these changes had on the total CO2 reported by an NGL fractionator depends on the mixture of products the plant supplies and whether the fractionator used the default value or a measured value. Since most NGL fractionators supply ethane, the reported CO2 across the industry was lower beginning in 2013 than would have been reported if the factors had not been updated.

[1]     U.S. Department of Energy, Energy Information Administration, U. S. Energy Information Administration/Petroleum Supply Annual 2019, Volume 1, Table 15. Natural Gas Plant Net Production and Stocks of Petroleum Products by PAD and Refining Districts, 2019, August 31, 2020. Available at:

[2]     U.S. Department of Energy, Energy Information Administration, This Week in Petroleum, In 2020, Increased Propane, Other HGL Exports Contribute to Continued Strong Product Exports Despite Reductions in Major Transport Fuels, September 23, 2020. Available at: https://www.eia.gov/petroleum/weekly/archive/2020/200923/includes/analysis_print.php.

[3]     U.S. Department of Energy, Energy Information Administration, The United States Exported More Propane than Distillate in 2020, March 8, 2021. Available at: https://www.eia.gov/todayinenergy/detail.php?id=47036

[4]      U.S. Department of Energy, Energy Information Administration, Hydrocarbon Gas Liquids Explained, October 31, 2019. Available at: https://www.eia.gov/energyexplained/hydrocarbon-gas-liquids/prices-for-hydrocarbon-gas-liquids.php

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