Renewable Natural Gas

What is Natural Gas?

Natural Gas is a fossil energy that contain many different compounds, the majority of which is methane, a hydrocarbon containing one atom of carbon and four atoms of hydrogen (CH4). Other compounds found in natural gas are hydrocarbon gas liquids, water vapor, and carbon dioxide. Natural gas can be found in large cracks and spaces between layers of overlying rocks. This type of natural gas is called conventional natural gas. Other source of natural gas are shale, sandstone, and other types of sedimentary rocks. Natural gas extracted from these sources is called unconventional natural gas while those extracted from crude oil deposits are called associated natural gas.1

Natural Gas as a transportation fuel

Because of its lower greenhouse gas emissions and its inherently lower price than gasoline and diesel, natural gas has been considered an alternative fuel.2 Vehicles can be upfitted to run on both conventional fuel and natural gas without undergoing costly conversion. Natural gas is used in transportation in the form of compressed natural gas (CNG) or liquefied natural gas (LNG). Recent developments in fuel storage technology have introduced the use of adsorbed natural gas (ANG) in transportation in a commercial scale.3,4,5 ANG technology operates at considerably lower pressure than that of CNG and allows refilling at 900 psi instead of 3600 psi.6,7

A well-to-wheel (WTW) analysis of natural gas conducted by the Energy Systems Division of Argonne National Laboratory showed that it yields 14% less CO2 equivalent (CO2e) per Megajoule than gasoline. In the same study, the waste-to-well analysis of renewable natural gas sourced from anaerobic digestion of animal waste showed 82 to 91% reduction GHG emission reduction versus gasoline and 86 to 94% reduction versus diesel.8 

What is Renewable Natural Gas (RNG)?

Renewable Natural Gas or RNG is an upgraded or refined biogas produced from a variety of renewable sources including solid waste landfills, water treatment facilities, livestock farms, waste from food and beverage production, and organic waste management operations.9,10 Compared to conventional natural gas (derived from fossil), RNG has zero to very low amounts of other hydrocarbons such as ethane, propane, butane, and pentane.11

RNG reduces methane emissions significantly in that it captures methane that would otherwise be released to the atmosphere from landfills and other industrial and agricultural wastes. Methane has a significantly higher global warming impact than CO2, about 25 times more potent.12 Based on waste-to-well studies conducted by Argonne National Laboratory, RNG sourced from landfills produces 80 to 82% lower CO2e emissions per MJ versus gasoline, and 77% versus diesel.13 The following table summarizes the WTW GHG emission of RNG from different sources based on studies conducted by Argonne National Laboratory.


RNG Source (as CNG)

WTW GHG Emission Reduction

vs fossil gasoline

vs fossil diesel


80 to 100%

77 to 97%

Animal Waste15

82 to 91%

86 to 94%

Sludge Wastewater Treatment Plant16

94 to 193%

no data

Table source: CSB author based on references cited

Learn more >> Renewable Natural Gas Webinar

This virtual event was co-hosted by the Carnegie Mellon University Wilton E. Scott Institute for Energy Innovation. Industry leaders and academia experts came together for a moderated energy panel on renewable natural gas. Panelists included Marc Fetten, CEO of GreenGasUSA, Sharon Frank, VP of Environmental, Health & Safety, Montauk Renewables, Inc., Sam Lehr, Policy Manager at The Coalition for Renewable Natural Gas, Götz Veser, Professor at the University of Pittsburgh Swanson School of Engineering, and Larry Frederick, PTAC SC. Guest Speakers and Moderators included Katelyn Haas-Conrad, Assistant Director at the CMU Scott Institute for Energy Innovation, and Chris Gassman, Associate Director at the University of Pittsburgh Center for Sustainable Business. Watch the full recording here.

With fugitive methane emissions, is RNG climate-positive or climate-negative?

While natural gas is considered a viable accelerator of the transition to clean energy, reservations on scaling up the use of this fuel arise because of fugitive emissions coming from leakages in its production, storage, and delivery, and its end use in transportation. Murphy and Holstein (2021) of the Environmental Defense Fund cited research conducted by Weller et al. (2020) where they estimated around 630,000 leaks in the natural gas distribution system in the U.S. resulting to 690,000 metric tons of methane emissions per year.17 This figure is five times higher than the estimates published in US EPA greenhouse gas inventory.18

Grubert (2020) evaluated the GHG intensity of RNG as the amount of methane leakage, on the assumption that combustion GHG emission of RNG is climate neutral. She classified the GHG intensity of RNG for three production pathways: (1) RNG produced from waste methane that would have otherwise been released to the atmosphere [as methane]; (2) RNG produced from waste methane that would have otherwise been flared off [i.e. burned in a flaring facility and released as carbon dioxide]; and (3) intentionally produced methane. In the assumption that burning RNG is carbon neutral, i.e., the carbon that was previously captured by the RNG source(s) is returned to the atmosphere as carbon dioxide, Pathway 1 is considered highly GHG negative [or climate positive]. Pathway 2 will only be GHG negative if the total leakage of the whole RNG system, that is to say leakage from production, storage, and transportation of RNG, is lower than the leakage from the flare. For comparison, leakage from flare is estimated at 1% while leakage in the downstream of production alone is already estimated at 0.8%. Thus, Grubert, E. assessed Pathway 2 as highly unlikely to be GHG negative [or climate-positive]. For Pathway 3, since methane is intentionally produced as opposed to no methane produced, any system leakage makes it GHG-positive [or climate-negative].19 To curb methane emissions from the pipeline, the U.S. senate has passed the Protecting our Infrastructure of Pipelines and Enhancing Safety or PIPES Act of 2020 in August of 2020. The Act focuses on setting standards to reduce methane emissions from all three pipeline categories: gathering lines, long distance transmission lines, and local distribution lines.20 It also details the appropriations for pipeline safety programs and requires adoption of advanced leak detection technologies and practices.21

The end use of methane in transportation is also seen as a significant contributor to methane emissions, specifically from the tailpipes, engine crankcase,22 and filling of compressed natural gas.23 While there is not an abundance of resource on the pump-to-wheels (PTW) methane emissions of natural gas systems, researchers from West Virginia University have developed a novel measurement system to quantify methane leaks and conducted a pilot study on heavy duty transportation sector. Based on this study, engine crankcase methane emissions contributed 39% while engine tailpipes, 30% of the total PTW emissions. Vehicle and station tanks combined accounted for 8% of the total PTW emissions.24 Opportunely, EPA has recently certified the use of engines with closed crankcases which addresses the emission problems from engine crankcase.25 The following chart from Clark et al. (2016) shows the absolute (in g methane loss per kg of fuel used) and relative contribution of different sources to the total PTW emissions.

From: Clark, N. et al. (2016, December 22). Pump-to-Wheels Methane Emissions from the Heavy-Duty Transportation Sector. Environmental Science & Technology, 51, 968-976. doi:10.1021/acs.est.5b06059

Does investment in renewable natural gas deter the development of electric alternatives?

In the country's journey towards zero emission in 2050, an optimal combination of different pathways and technologies will be necessary instead of a single “all in” approach. In the process of transitioning to zero emission technologies, RNG can serve as a displacement fuel to fossil fuels and for some geographical and sectoral areas that are difficult to decarbonize or electrify, RNG can play a significant role as well.26 In a study done for the California Air Resources Board, Mahone et al. (2018)27 concluded that biomethane, alongside hydrogen or synthetic fuels, is a pillar upon which cross-sector decarbonization could be achieved. For instance, RNG can displace additional gas demand for buildings, while in the transport sector, compressed biomethane sees more utility in medium and heavy-duty vehicles as the LDV segment tilts more towards electrification.

Cyrs, T. et al (2020) from World Resources Institute (WRI) summarized multiple studies on the role of RNG in Deep Decarbonization in the following table. From these studies, it can be deduced that RNG will play a significant role in achieving net zero and is complementary to electrification. Investing in the development and deployment of RNG as well as the assoiciated infrastucture, therefore, does not and should not hamper electrification of geographical and sectoral areas where electrification proves to be the best alternative.





Deep Decarbonization in a High Renewables Future

(Mahone et al. 2018)29

Transport: Light-duty vehicles move toward 100% electrification. Medium- and heavy-duty vehicles use biomethane alongside mix of CNG, hydrogen, and other biofuel options.

Stationary end uses: Alongside large-scale building electrification, RNG displaces additional building gas demand.


Getting to Neutral: Options for Negative Emissions in California

(Baker et al. 2020)30

Cross-cutting: Reaching net-zero emissions will require scaling of net-negative decarbonization strategies. RNG and hydrogen from organic wastes can play a role if coupled with emerging CCS technologies to achieve added carbon removal.

Oregon/ Washington

Pacific Northwest Pathways to 2050

(Aas et al. 2018)31

Stationary end uses: Alongside electrification efforts, RNG and hydrogen may be used in existing gas distribution networks to help decarbonize hard-to-abate end uses and meet peak heating demand.


Northeastern Regional Assessment of Strategic Electrification

(Hopkins et al. 2017)32

Cross-cutting: Alongside rapid electrification, RNG and other low-carbon fuel supply can be deployed to further lower emissions.


Northeast 80x50 Pathway

(National Grid 2018)33

Stationary end uses: Region can reduce emissions through rapid transition away from liquid fuels in building heating and conversion to electric heat pumps, natural gas, and renewable natural gas from local feedstocks.


The Role of Renewable Biofuels in a Low Carbon Economy (Lowell and Saha 2020)34

Cross-cutting: Complementary deployment of biofuels may be viable for decarbonization.

Transport: Alongside significant electrification of heavy-duty vehicles (with the exception of combi­nation trucks), RNG fuels 80–100% of NG vehicles in 2030.

Stationary end uses: Alongside electrification, RNG may be used to meet 5–10% of residential and commercial heating demand in 2030.

from: Renewable Natural Gas as a Climate Strategy: Guidance for State Policymakers. Working Paper.  Cyrs, T., Feldmann, J., Gasper, R. (2020, December). World Resources Institute:Washington, DC


Natural gas explained. (2021, December 2), U.S. Energy Information Administration.
Semin, R. A. B. (2008). A technical review of compressed natural gas as an alternative fuel for internal combustion engines. Am. J. Eng. Appl. Sci, 1(4), 302-311.
3 Adsorbed Natural Gas. (n.d.). Altech-Eco. accessed on 18 January 2022.
4 Atlanta Gas Light to Test Adsorbed Natural Gas Technology for Light-Duty Trucks. (2019, May 29). Southern Company.
5 City of Orlando partners with Ingevity to pilot demonstration fleet of adsorbed natural gas trucks. (2021, February 23). Businesswire.
6 Dziewiecky, M. (2018). Adsorbed Natural Gas Tan feeded with Liquid Natural Gas. E3S Web of Conferences, 44, 00038. doi:10.1051/20184400038
7 Atlanta Gas Light (n 4)
8 Han, J, Mintz, M, & Wang, M. (2011, December 14). Waste-to-wheel analysis of anaerobic-digestion-based renewable natural gas pathways with the GREET model. United States.
9 Renewable Natural Gas from Agriculture-Based AD/Biogas Systems. (n.d.). United States Environmental Protection Agency.
10 US EPA (2020, July). An Overview of Renewable Natural Gas from Biogas. EPA 456-R-20-001. accessed on 24 Nov 2021.
11 Renewable Natural Gas. (n.d.) United States Environmental Protection Agency.
12 ibid.
13 Mintz, M, Han, J, Wang, M, Saricks, C, & Energy Systems. (2010). Well-to-Wheels analysis of landfill gas-based pathways and their addition to the GREET model. United States. 33-34.
14 ibid.
15 Han, J, Mintz, M, & Wang, M. (n 8).
16 Lee, U. et al. (2016, September 1). Lifecycle Analysis of Renewable Natural Gas and Hydrocarbon Fuels from Wastewater Treatment Plant’s Sludge. United States. 22-28.
17 Murphy, E., & Hosltein, E. (2021, July 6). Federal pipeline agency has essential opportunity to reduce methane emissions. Retrieved from EDF: on 21 March 2022
18 Weller, Z. D., Hamburg, S. P., & von Fischer, J. C. (2020). A National Estimate of Methane Leakage from Pipeline Mains in Natural Gas Local Distribution Systems. Environmental Science & Technology, 8598-8967.
19 Grubert, E. (2020, August 11). At scale, renewable natural gas systems could be climate intensive: the influence of methane feedstock and leakage rates. p3. IOP Publishing Ltd. accessed on 18 March 2022
20 Murphy, E., & Hosltein, E. (2021, July 6). (n 17)
21 S.2299 - 116th Congress (2019-2020): Protecting our Infrastructure of Pipelines and Enhancing Safety Act of 2020 or the PIPES Act of 2020.
22 Rudek, J., & Mathers, J. (2017, January 6). New Study Improves Understanding of Natural Gas Vehicle Methane Emissions, But Supply Chain Emissions Loom Large. Retrieved from EDF: accessed on 23 March 2022.
23 Sims R., R. Schaeffer, F. Creutzig, X. Cruz-Núñez, M. D’Agosto, D. Dimitriu, M.J. Figueroa Meza, L. Fulton, S. Kobayashi, O. Lah, A. McKinnon, P. Newman, M. Ouyang, J.J. Schauer, D. Sperling, and G. Tiwari, 2014: Transport. In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
24 Clark, N. N., McKain, D. L., Johnson, D. R., Wayne, W., Li, H., Akkerman, V., . . . Ugarte, O. J. (2016, December 22). Pump-to-Wheels Methane Emissions from the Heavy-Duty Transportation Sector. Environmental Science & Technology, 51, 968-976. doi:10.1021/acs.est.5b06059
25 Rudek, J., & Mathers, J. (2017, January 6). (n 22).
26 Cyrs, T., Feldmann, J., Gasper, R. (2020, December). Renewable Natural Gas as a Climate Strategy: Guidance for State Policymakers. Working Paper. Washington, DC: World Resources Institute. Available online at
27 Mahone, A. et al. (2018, June). Deep Decarbonization in a High Renewables Future: Updated Results from the California Pathways Model. San Francisco, CA: Energy and Environmental Economics, Inc. Available online at
28 Frequent Questions about Landfill Gas. (n.d.). United States Environmental Protection Agency.
29 Mahone, A. et al. (n 27).
30 Baker, S., J. Stolaroff, G. Peridas, S. Pang, H. Goldstein, F. Lucci, and W. Li. 2020. “Getting to Neutral: Options for Negative Carbon Emissions in California.” Livermore, CA: Lawrence Livermore National Laboratory.
31 Aas, D., S. Bharadwaj, A. Mahone, Z. Subin, T. Clark, S. Price. 2018. “Pacific Northwest Pathways to 2050: Achieving an 80% Reduction in Economy-Wide Greenhouse Gases by 2050.” San Francisco: Energy+Environmental Economics.
32 Hopkins, A., A. Horowitz, P. Knight, K. Takahashi, T. Comings, P. Kreycik, N. Veilleux, and J. Koo. 2017. Northeastern Regional Assessment of Strategic Electrification. Lexington, MA: Northeast Energy Efficiency Partnerships (NEEP).
33 National Grid. 2018. “Northeast 80x50 Pathway.”
34 Lowell, D., and A. Saha. 2020. “The Role of Renewable Biofuels in a Low Carbon Economy.” Washington, DC: M.J. Bradley and Associates, LLC.