For suppliers of natural gas liquids, the reported 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 458 MMT in 2021. 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 reported 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, and increased exports. [2, 3, 4] Production capacity increased due to construction of new fractionation plants (124 plants in 2020 compared with 116 in 2011) and increased production at existing plants. The ratio of CO₂ to number of plants reporting has increased from 2.52 MMTCO₂/plant in 2011 to 3.96 MMTCO₂ /plant in 2021. Although the number of plants reporting in 2021 decreased from a high of 124 in 2020 to 119, the CO₂ per plant increased from 3.59 MMTCO₂/plant in 2020 to 3.96 MMTCO₂ /plant in 2021. The year-over-year increases in the CO₂ emissions from NGLs were approximately 12 percent for 2018 and 2019, 8 percent for 2020 and 6 percent for 2021. Domestic consumption of NGLs increased by 53 percent from 2.25 million barrels per day in 2011 to 3.44 million barrels per day in 2021 (53 percent increase). [4] For example, increases in ethane supply between 2017 and 2021 are in part a response to the completion of new petrochemical facilities in the U.S. that use ethane as a feedstock. [5] However, the increase in annual NGL production reported in recent years is driven primarily by increases in exports due to high international demand and expansion of U.S. export facilities through the construction of new pipelines and export terminals. [2, 3, 4]. The U.S. currently produces more NGLs than it consumes on an annual basis. Exports of NGL products increased from 0.25 million barrels a day in 2011 to 2.31 million barrels per day in 2021 (824 percent). [4] Although exports of all NGLs have increased over the decade, exports of propane have increased the most and make up the largest share of total NGL exports. Exports of propane increased from 0.17 million barrels per day in 2012 to 1.33 million barrels per day in 2021 driven by strong market demand in Asia. [3, 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: https://www.eia.gov/petroleum/supply/annual/volume1/pdf/table15.pdf.

[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: Imports and Exports of Hydrocarbon Gas Liquids, September 13, 2022. Available at: https://www.eia.gov/energyexplained/hydrocarbon-gas-liquids/imports-and-exports-of-hydrocarbon-gas-liquids.php.

[5]     U.S. Department of Energy, Energy Information Administration, Hydrocarbon Gas Liquids Explained: Prices of Hydrocarbon Gas Liquids, January, 2022. Available at: https://www.eia.gov/energyexplained/hydrocarbon-gas-liquids/prices-for-hydrocarbon-gas-liquids.php.