Fact-checked by Grok 2 weeks ago

Gasoline gallon equivalent

The gasoline gallon equivalent (GGE) is a standardized used to compare the energy content of alternative fuels to that of one U.S. liquid of , defined as containing 114,300 British thermal units (Btu) of lower heating value. This equivalence facilitates fair assessments of , costs, and environmental impacts across different sources in and other applications. GGE is primarily employed by government agencies, fuel providers, and vehicle manufacturers to report fuel economy, set pricing at dispensers, and comply with regulations such as the Energy Policy Act of 1992, which promotes alternative fuels for fleet vehicles. For taxation and sales purposes, alternative fuels like (CNG) are often measured and taxed on a GGE basis, ensuring equitable treatment relative to conventional . Similarly, diesel gallon equivalent (DGE) serves a parallel role for , equating to 128,700 Btu per gallon to account for diesel's higher energy density. Common GGE conversions for key alternative fuels, based on their lower heating values, include: These values enable consumers and policymakers to evaluate alternatives like electric vehicles or fleets on an apples-to-apples basis with gasoline-powered options, supporting the transition to lower-emission transportation.

Definition and Purpose

Core Definition

The (GGE) is defined as the amount of an alternative fuel necessary to supply the equivalent to one U.S. of . This unit enables standardized comparisons of diverse fuels by focusing on their content rather than or . Energy content serves as the foundational principle for GGE, typically quantified in British thermal units (BTU), where one gallon of gasoline provides approximately 112,000 to 116,000 BTU depending on the ethanol blend, such as E10. By normalizing fuels like compressed natural gas or electricity to this gasoline benchmark, GGE allows for equitable evaluation of their performance in transportation applications, where energy delivery directly influences vehicle range and efficiency. This approach accounts for inherent differences in fuel densities and forms, promoting informed decisions on alternative energy sources without bias toward liquid gasoline. The GGE metric was standardized in 1994 by the National Institute of Standards and Technology (NIST) to facilitate adoption, aligning with requirements of the Energy Policy Act of 1992, which aimed to reduce petroleum dependence through promotion of non-petroleum-based transportation fuels. It underpins related efficiency measures, such as miles per gallon equivalent (MPGe), for assessing vehicle fuel economy across fuel types.

Historical Development and Usage

The concept of the gasoline gallon equivalent (GGE) originated amid the 1970s oil crises, particularly the 1973 Arab oil embargo, which exposed U.S. vulnerabilities to foreign supplies and spurred federal efforts to develop and standardize alternative fuels for transportation. These events, combined with the 1979 energy crisis, accelerated research into non- options like and biofuels, necessitating a common metric to evaluate their energy equivalence to for fair comparisons in efficiency and cost. GGE was formalized in 1994 through guidelines issued by the National Institute of Standards and Technology (NIST), defining it as a standardized energy-based unit to facilitate the adoption of alternative fuels in vehicles. This development aligned with the Energy Policy Act of 1992 (), which mandated federal fleet acquisitions of alternative fuel vehicles and required measurement of fuel use in gasoline-equivalent terms to promote broader . In policy and industry contexts, GGE has been integral to federal regulations, including EPAct-mandated fleet requirements for state governments, providers, and federal agencies, where compliance is tracked via annual reports of consumption in GGE units. It supports incentives such as the Refueling Property Credit under the , encouraging infrastructure for and other alternatives, while aiding fuel labeling standards to inform consumer choices on . Overall, GGE has played a key role in advancing U.S. by enabling equitable assessments of diverse fuels in transportation sectors. The metric's evolution in the 2010s incorporated updates for biofuels and electric vehicles under (CAFE) standards, with DOE refining petroleum-equivalent calculations to better integrate energy content from these sources into . Notably, the Environmental Protection Agency (EPA) integrated GGE-based miles per gallon equivalent (MPGe) ratings into fuel economy labels starting in 2011 for , plug-in, and electric vehicles, allowing direct comparisons with conventional models. This shift emphasized energy-based equivalence over volumetric measures, accommodating varying fuel densities and supporting CAFE goals for reduced oil dependence.

Calculation and Methodology

Energy Content Determination

The energy content of fuels, which forms the foundation for gasoline gallon equivalent (GGE) calculations, is primarily determined through calorimetric measurements that quantify the heat released during combustion. The most common technique is bomb calorimetry, where a small sample of the fuel is ignited in a sealed, oxygen-filled bomb under constant volume conditions, allowing the total heat of combustion to be measured precisely. This method adheres to standards such as ASTM D240 or D4809, which outline procedures for liquid hydrocarbon fuels, including aviation turbine fuels and applicable blends. For oxygenated fuels like ethanol blends, adjustments to these methods or estimation techniques such as ASTM D4868 may be used to assess heat of combustion consistently. A critical distinction in energy content determination is between the higher heating value (HHV) and the lower heating value (LHV). The HHV includes the of from water produced during combustion, assuming complete condensation, while the LHV excludes this, reflecting the available when water remains as vapor—conditions typical in internal combustion engines. GGE calculations standardize on the LHV to better represent real-world usable in applications, as engine exhaust does not typically allow water condensation to recover that . Bomb calorimeters directly measure the HHV, from which the LHV is derived by subtracting the contribution based on the fuel's content and standard vaporization enthalpies. For baseline consistency in GGE comparisons, the U.S. Department of Energy (DOE) uses an average LHV of 114,102 BTU per gallon for E10 gasoline, the current standard reference fuel (historical certification fuels like indolene had ~114,118 BTU/gal). This value, within the range of 112,114–116,090 BTU/gal for typical gasoline compositions, enables equitable benchmarking against alternative fuels. However, actual energy content varies due to factors such as fuel composition—e.g., ethanol blends reduce LHV because ethanol has a lower energy density than pure hydrocarbons—temperature, which affects fuel density and thus volumetric energy, and pressure, which influences gaseous fuels more significantly but can alter liquid compressibility in high-precision measurements. ASTM standards like D4809 mitigate these variabilities by specifying controlled conditions for testing, including sample preparation and correction factors for non-ideal combustion products.

Conversion Factors and Formulas

The Gasoline Gallon Equivalent (GGE) is the amount of an alternative fuel—with the same energy content (using LHV) as one gallon of gasoline—to enable direct comparisons of fuel energy across different types. The core formula for the amount of alternative fuel required to equal one gallon of gasoline is: \text{Amount of alternative fuel per GGE} = \frac{\text{Energy content of gasoline (BTU per gallon)}}{\text{Energy content of alternative fuel (BTU per unit)}} The content of is set at 114,102 BTU per based on the LHV for E10 blends. This approach yields the units (e.g., gallons, pounds, or standard cubic feet at 60°F and 14.73 psia for gases) of the needed to match one of 's . Conversion factors account for variations in fuel states and measurement units, such as standard cubic feet (scf) for gases versus gallons for liquids. For (CNG), the content is 20,160 BTU per with a density of 0.0458 pounds per scf, yielding approximately 924 BTU per scf; thus, the factor is 114,102 BTU/ ÷ 924 BTU/scf ≈ 123.57 scf per GGE. multipliers are incorporated to address non-ideal transfer in internal combustion engines, including adjustments for factors like and heat losses. For liquid alternative fuels, the equation matches volumetric energy densities directly. For ethanol, with an LHV of 76,330 BTU per gallon: \text{Gallons of ethanol per GGE} = \frac{114,102 \text{ BTU/gallon (gasoline)}}{76,330 \text{ BTU/gallon (ethanol)}} \approx 1.49 or equivalently, 1 gallon of ethanol equals approximately 0.67 GGE. Adjustments for real-world performance include volumetric efficiency factors, such as 0.949 for liquefied natural gas (LNG) to compensate for energy losses during vaporization and engine operation. The U.S. Department of Energy (DOE) maintains official factor tables through the Alternative Fuels Data Center, incorporating refined LHV data and methodology updates to ensure accuracy in equivalency calculations; detailed factors for specific fuels are provided in DOE references.

Applications in Efficiency Metrics

Miles per Gallon Equivalent (MPGe)

Miles per gallon equivalent (MPGe) is a metric developed by the U.S. Environmental Protection Agency (EPA) to measure the fuel economy of vehicles, such as electric vehicles (EVs), electric vehicles (PHEVs), and flexible fuel vehicles (FFVs), by expressing efficiency in terms of miles traveled per gasoline gallon equivalent (GGE). This standardization enables direct comparisons between these vehicles and conventional gasoline-powered ones by converting the energy consumed from sources like or other s into an equivalent amount of gasoline energy, where 1 GGE corresponds to approximately 33.7 kilowatt-hours (kWh) of . The calculation of MPGe relies on EPA's five-cycle laboratory testing procedures, which assess vehicle performance under simulated city and highway driving conditions until the energy source is depleted, incorporating a wall-to-wheel that accounts for delivery from the power (e.g., electrical outlet) to the vehicle's wheels, including charging losses for EVs. For electricity-powered vehicles, MPGe is computed as 33.705 kWh per gallon divided by the vehicle's electricity consumption in kWh per mile, or equivalently, miles driven divided by (total consumed in kWh divided by 33.705). For PHEVs, the metric weights electric and gasoline modes using utility factors derived from real-world driving data to yield a combined value. This approach was introduced by the EPA in as part of revised economy labeling regulations to fulfill requirements under the for advanced technology vehicles. For example, the 2022 rear-wheel-drive model achieved an EPA-rated combined MPGe of 132, demonstrating how the metric highlights the higher efficiency of EVs compared to typical vehicles with 20-30 miles per (). Unlike traditional , which measures only tailpipe-to-wheel efficiency for liquid fuels and cannot apply to electricity-based systems, MPGe provides a more comprehensive view by normalizing diverse energy inputs, thereby revealing source-to-wheel losses such as those in electrical charging and better informing consumer choices on efficiency and costs.

Fuel Economy Comparisons

Gasoline gallon equivalent (GGE) provides a standardized framework for comparing fuel economy across diverse types and s by normalizing energy content to that of , enabling evaluations of metrics such as cost per mile and equivalence. For instance, in fleet operations, GGE facilitates direct assessments of ; in a 1999 study by the on a fleet, CNG models achieved fuel costs of 4.35 cents per mile compared to 6.39 cents per mile for equivalents, representing more than a 30% reduction when adjusted for energy content. This normalization allows fleet managers to project on a common basis, such as estimating that a CNG with a 200-mile per GGE tank matches the effective travel distance of a under similar conditions. In regulatory contexts, GGE plays a key role in (CAFE) standards for multi-fuel vehicles by adjusting for differences in , ensuring equitable compliance calculations. For dual-fuel vehicles capable of operating on gasoline and s like , CAFE credits convert alternative fuel consumption into gasoline-equivalent gallons, where one of gaseous fuel is equated to its GGE value through equivalency factors. This adjustment accounts for the lower of alternatives, preventing over- or underestimation of fleet-wide ; for example, dual-fuel automobiles report fuel economy in miles per equivalent to align with gasoline benchmarks. In hybrid systems, such as plug-in hybrids, GGE-based -equivalent fuel economy (PEFE) methodologies weight electrical and contributions, applying revised equivalency values (e.g., 79,989 watt-hours per for model year 2027) to reflect grid and variances. The U.S. Department of 's Vehicle Cost Calculator exemplifies GGE's application in practical fuel economy assessments, allowing users to estimate annual fuel costs by inputting driving habits like 11,926 miles per year split between city and highway. This tool compares up to eight models across fuel types, incorporating GGE conversions to compute total ownership costs and emissions on an energy-equivalent basis, with updates reflecting 2023 fuel price data for accurate projections. For a typical , it might show annual costs at $1,500 versus $1,200 for a CNG equivalent, highlighting savings when scaled to fleet use. Despite its utility, GGE comparisons have limitations, as they focus solely on energy content and overlook non-energy factors such as refueling time and infrastructure availability. Alternative fuels like often require longer refueling durations—up to several hours at time-fill stations versus minutes for —potentially increasing operational downtime in fleet scenarios without capturing these inefficiencies in energy-based metrics. Additionally, sparse refueling networks can limit equivalence in practice, even when GGE suggests parity, emphasizing the need for holistic evaluations beyond pure adjustments. While metrics like miles per gallon equivalent (MPGe) offer a related measure, GGE extends to broader and analyses essential for decision-making.

Equivalents for Specific Fuels

Compressed Natural Gas (CNG)

(CNG) serves as a key in the context of gasoline gallon equivalents (GGE), where one GGE represents the quantity of CNG with equivalent to one U.S. of , 114,300 British thermal units (Btu). The U.S. Department of (DOE) establishes this equivalency at 5.66 of mass or 123.57 (scf) of CNG, derived from the lower heating value of (20,160 Btu per pound) and its (0.0458 pounds per standard cubic foot), yielding about 924 Btu per scf. This standard accounts for typical pipeline-quality natural gas compositions, though variations in —ranging from 900 to 1,000 Btu/scf—can adjust the precise volume slightly across different calculations. A distinctive feature of CNG in GGE applications is its compression to 3,000–3,600 pounds per () for onboard vehicle storage, which condenses the gas from its measure into a much smaller volume, influencing practical fueling and tank design considerations. Composed mainly of , CNG exhibits clean-burning characteristics that result in reduced emissions of pollutants like nitrogen oxides and relative to , enhancing its appeal for environmental in GGE-based efficiency assessments. In transit bus operations, CNG adoption leverages GGE metrics to demonstrate fuel economy, often yielding 20–30% cost savings over equivalents through lower per-GGE pricing, as evidenced in fleet evaluations where costs averaged 25–50 cents less per GGE than conventional fuels. However, the compressed storage system's volumetric constraints limit typical vehicle ranges to 200–300 miles per tank, necessitating strategic refueling infrastructure to support broader deployment.

Ethanol Blends (E85)

Ethanol, a biofuel commonly derived from corn, serves as a key component in gasoline blends, with the gasoline gallon equivalent (GGE) providing a standardized measure of its energy content relative to conventional . Pure has an energy content of approximately 76,100 BTU per , requiring about 1.5 gallons of pure ethanol to match the energy of one of (which averages 114,000 BTU per ). For E85, a blend consisting of 85% ethanol and 15% , the GGE value is approximately 1.28 gallons per GGE, as one of E85 delivers about 78% of the energy in one of . The integration of ethanol blends like into the supply highlights unique challenges and benefits related to and environmental impact. 's lower volumetric —about 70% that of —necessitates adjustments in flex-fuel vehicles (FFVs), which are engineered with specialized systems, sensors, and engine calibrations to optimize performance across varying ethanol concentrations and mitigate issues like and cold-start difficulties. Additionally, corn-derived ethanol's lifecycle are estimated to be 21% lower than those of on average, accounting for farming, , , and , though this can vary based on agricultural practices and coproduct credits. In regulatory contexts, the GGE framework supports compliance with biofuel mandates, such as the U.S. Environmental Protection Agency's (EPA) partial waiver issued in 2010, which permitted (15% blend) for use in model year 2007 and newer light-duty vehicles, expanding blending options beyond E10. Under the Renewable Fuel Standard (RFS), GGE values aid in verifying energy equivalence for blends up to 10-15%, ensuring that mandated volumes contribute effectively to renewable fuel goals without undermining overall . Practically, vehicles tuned for operation experience a 25-30% reduction in miles per (MPG) compared to due to the blend's lower content, but this is often offset by E85's lower pump price—typically 20-30% less per —potentially yielding cost savings when evaluated on a per-mile or GGE basis.

References

  1. [1]
    Glossary - Alternative Fuels Data Center - Department of Energy
    Gasoline Gallon Equivalent. The amount of fuel it takes to equal the energy content of one liquid gallon of gasoline where one gasoline gallon equivalent (GGE) ...
  2. [2]
    Fuel Properties Comparison - Alternative Fuels Data Center
    1 gallon of gasoline has 97%–100% of the energy in 1 GGE. Standard fuel is 90% gasoline, 10% ethanol. 1 gallon of diesel has 113% of the energy in 1 GGE due to ...
  3. [3]
    Fuel Conversion Factors to Gasoline Gallon Equivalents
    Fuel Conversion Factors to Gasoline Gallon Equivalents ; Electricity, kWh, 0.03, GGE = Electricity kWh x 0.03 ; Gasoline, Gallons, 1.00, GGE = Gasoline gal x 1.Missing: definition | Show results with:definition
  4. [4]
    Gasoline and Diesel Gallon Equivalent Definition
    Motor fuels, including alternative fuels, may be sold by gasoline gallon equivalent (GGE) or diesel gallon equivalent (DGE) as long as the dispenser used for ...
  5. [5]
    Gasoline and Diesel Gallon Equivalency Methodology
    Compressed Natural Gas. Gasoline (E10): LHV Range = 112,114 ← → 116,090 Btu/gal ... The AFDC is a resource of the U.S. Department of Energy's Vehicle Technologies ...
  6. [6]
    British thermal units (Btu) - U.S. Energy Information Administration ...
    Natural gas, 1 cubic foot=1,036 Btu · 1 therm=100,000 Btu ; Motor gasoline, 1 gallon=120,214 Btu ; Diesel fuel, 1 gallon=137,381 Btu ; Heating oil, 1 gallon=138,500 ...
  7. [7]
    Key Federal Legislation - Alternative Fuels Data Center
    The Energy Policy Act (EPAct) of 1992 (Public Law 102-486 ) aims to reduce U.S. dependence on petroleum and improve air quality by addressing all aspects of ...Missing: GGE introduction
  8. [8]
    Electric Vehicle Benefits and Considerations
    Miles per gallon of gasoline equivalent (MPGe) and kilowatt-hours (kWh) per 100 miles are common metrics. Depending on how they are driven, today's light ...<|control11|><|separator|>
  9. [9]
    History of gasoline - U.S. Energy Information Administration (EIA)
    Dec 22, 2023 · Unleaded gasoline was introduced in the 1970s when health problems from lead became apparent. In the United States, leaded gasoline for use ...
  10. [10]
    [PDF] RCED-94-161 Alternative-Fueled Vehicles - GAO
    Jul 15, 1994 · The Energy Policy Act of 1992 requires that federal and state fleets and alternative fuel providers purchase an increasing percentage of.
  11. [11]
    H.R.776 - 102nd Congress (1991-1992): Energy Policy Act of 1992
    Directs the Secretary of Energy (the Secretary) to establish a public information program on the use of alternative fuels in motor vehicles. Requires the ...Missing: GGE | Show results with:GGE
  12. [12]
    10 CFR Part 490 -- Alternative Fuel Transportation Program - eCFR
    The provisions of this part implement the alternative fuel transportation program for State government and alternative fuel provider fleets.
  13. [13]
    [PDF] Alternatives to Traditional Transportation Fuels 1994
    By 1996, alternative and replacement fuels are expected to account for 3.1 percent of the fuel used (on a gasoline- equivalent gallon basis) in highway vehicles ...
  14. [14]
    Petroleum-Equivalent Fuel Economy Calculation - Federal Register
    Mar 29, 2024 · This final rule revises DOE's regulations regarding procedures for calculating a value for the petroleum-equivalent fuel economy of electric vehicles (EVs).
  15. [15]
    Revisions and Additions to Motor Vehicle Fuel Economy Label
    Jul 6, 2011 · The redesigned label provides expanded information to American consumers about new vehicle fuel economy and fuel consumption, greenhouse gas and smog-forming ...Missing: GGE | Show results with:GGE
  16. [16]
    EPA, DOT Unveil the Next Generation of Fuel Economy Labels
    Aug 1, 2019 · Fuel Economy: The label shows fuel economy for advanced technology vehicles in miles per gallon of gasoline-equivalent (MPGe). A gallon of ...
  17. [17]
    Bomb Calorimeter - an overview | ScienceDirect Topics
    The higher heating value (HHV) can be measured in a bomb calorimeter using ASTM standard D-2015 (withdrawn by ASTM 2000, and not replaced). The bomb calorimeter ...
  18. [18]
    HHV and LHV Calorific Values - DDS Calorimeters
    A calorimeter measures the High Heating Value (HHV) because the combustion is contained in a closed environment (The combustion vessel).
  19. [19]
    [PDF] Chapter 2 - Thermodynamics of Combustion
    Such an instrument is called a bomb calorimeter. A constant-volume analysis of the bomb calorimeter data is used to determine the heating value of a particular ...
  20. [20]
    [PDF] Alternative Fuels Data Center Fuel Properties Comparison
    Based on composition, E85's lower heating value varies from 83,950 to 95,450 Btu/gal. [6] Lithium-ion battery density of 400 Wh/l from Linden and Reddy, ...
  21. [21]
    Revisions and Additions to Motor Vehicle Fuel Economy Label
    Sep 23, 2010 · Applying this rating system to model year 2010 data would assign the ratings as follows for the sample vehicles listed. Of course, future ...
  22. [22]
    [PDF] The 2022 EPA Automotive Trends Report
    For a vehicle operating on electricity, mpge is calculated as 33.705 kW- hrs/gallon divided by the vehicle electricity consumption in kW-hrs/mile. For ...
  23. [23]
    FOTW #1257, September 26, 2022: Seventeen EV Models Achieved ...
    Sep 26, 2022 · The Tesla Model 3 in rear-wheel drive configuration achieved the highest rating for MY 2022 with 132 MPGe. Notes: EVs include only all-electric ...
  24. [24]
    [PDF] Alternative Fuel Price Report January 2025
    Jan 1, 2025 · We chose 114,300 Btu/gal for the E10 energy content, consistent with the Transportation Energy Data Book energy content of CNG, in GGEs. See.
  25. [25]
    [PDF] Alternative Fuels in CAFE Rulemaking | NHTSA
    One gallon is counted as 0.15 gallon of fuel. –. Gaseous fuels – Natural Gas/Hydrogen: •. Converted to a gallon gasoline equivalent (gge) through petroleum.
  26. [26]
    [PDF] Environmental Protection Agency - Alternative Fuels Data Center
    This requires that the fuel economy value units are in terms of miles per equivalent gallon of gasoline for natural gas-fueled automobiles.
  27. [27]
    Vehicle Cost Calculator - Alternative Fuels Data Center
    This tool uses basic information about your driving habits to calculate total cost of ownership and emissions for makes and models of most vehicles.
  28. [28]
    [PDF] Clean Cities Alternative Fuel Price Report, January 2024
    Jan 1, 2024 · Conversion factors used to establish prices in dollars per gasoline gallon equivalent ($/GGE) and dollars per diesel gallon equivalent ($/DGE) ...Missing: standard | Show results with:standard
  29. [29]
    [PDF] Alternative Refueling Infrastructure - California Energy Commission
    Natural gas costs are typically lower compared to gasoline on a gasoline gallon equivalent basis, and natural gas generally produces lower greenhouse gas.
  30. [30]
    Maps and Data - Average Annual Fuel Use by Vehicle Type
    This chart shows average annual fuel use (per vehicle) for major vehicle categories in the United States. The metric used is gasoline gallon equivalents (GGEs) ...Missing: tool | Show results with:tool
  31. [31]
    Lifecycle Greenhouse Gas Results | US EPA
    May 29, 2025 · This page provides a summary of the lifecycle greenhouse gas (GHG) analyses that EPA has undertaken for the US Renewable Fuel Standard (RFS) program.
  32. [32]
    E15 Fuel Partial Waivers | US EPA
    Partial waiver for E15 for use in MY2007 and newer light-duty motor vehicles (pdf) (4.6 MB, published November 4, 2010); Extension of Comment Period: Notice ...
  33. [33]
    Overview of the Renewable Fuel Standard Program | US EPA
    May 7, 2025 · The RFS program is a national policy that requires a certain volume of renewable fuel be used to replace or reduce the quantity of fossil fuel.
  34. [34]
    [PDF] Clean Cities Alternative Fuel Price Report, October 2019
    Oct 1, 2019 · 1.04%. NATIONAL AVERAGE. $3.04. $3.08. $0.04. 1.32%. TABLE 12a - Gasoline ... Compressed natural gas (in GGE), propane, and ethanol (E85) have ...