EPA/600/R-10/001 | January 2010 | www.epa.gov/athens 

Gasoline Composition Regulations 

Affecting 

LUST Sites

Ecosystems Research Division, Athens, GA 30605 

National Exposure Research Laboratory 

Office of Research and Development 
EPA 600/R-10/001 

January 2010 

Gasoline Composition Regulations Affecting 

LUST Sites 

by 

James W. Weaver, Linda R. Exum, Lourdes M. Prieto 

Ecosystems Research Division 

National Exposure Research Laboratory 

Office of Research and Development 

United States Environmental Protection Agency 

Athens, Georgia 30605 

U.S. Environmental Protection Agency 

Office of Research and Development 

Washington, DC 20460
Notice 

The U.S. Environmental Protection Agency, through its Office of Research and 

Development, funded and managed the research described here. It has been subjected to 

the Agency’s peer and administrative review and approved for publication as an EPA 

document. Mention of trade names or commercial products does not constitute 

endorsement or recommendation for use. The information provided in this paper is not 

intended to determine compliance with state or federal regulations for air quality, 

gasoline composition or similar purposes. For those purposes, information should be 

obtained from the appropriate local, state and federal regulatory agencies, the Clean Air 

Act, the United States Code, the Code of Federal Regulations, the Federal Register and 

other sources. 

2
Abstract 

Passage of the Clean Air Act Amendments in 1990 imposed requirements on 

gasoline composition in the United States. Impacts to ground water are affected by the 

provisions that required oxygenated additives and limited benzene concentration. 

Reformulated and oxygenated gasoline were required to contain an oxygenated additive 

at 2.0 wt % and 2.7 wt %, respectively. In most cases, the additive initially was methyl 

tert-butyl ether (MTBE). The amount of benzene in both reformulated and conventional 

gasoline was limited: reformulated gasoline contains less than 1 % benzene by volume, 

while benzene levels in conventional gasoline were set by producer baselines. The 

allowable benzene levels vary among these producers and, unlike reformulated gasoline, 

are not tied to use at specific locations in the U.S. In 2000, states began to pass bans on 

MTBE, other ethers, and/or alcohols; consequently, production and use of MTBE in 

reformulated gasoline declined. The Energy Policy Act of 2005 removed the oxygenate 

requirement from reformulated gasoline and industry responded by removing ethers from 

U.S. gasoline, with some limited exceptions. 

3
Foreword 

The National Exposure Research Laboratory’s Ecosystems Research Division 

(ERD) in Athens, GA conducts research on organic and inorganic chemicals, greenhouse 

gas biogeochemical cycles, and land use perturbations that create direct and indirect 

chemical and non-chemical stresses, exposures, and potential risks to humans and 

ecosystems. ERD scientists develop, test, apply and provide technical support for 

exposure and ecosystem response models that assess and manage risks to humans and 

ecosystems within a watershed /regional context. The Regulatory Support Branch (RSB) 

at ERD conducts problem-driven and applied research, develops technology tools, and 

provides technical support to customers in program and regional offices, states, 

municipalities, and tribes. Models are distributed and supported by EPA’s Center for 

Exposure Assessment Modeling (CEAM) and its Internet tools 

(www.epa.gov/athens/onsite). 

Research on gasoline composition is a fundamental part of assessing exposures to 

contamination from leaking underground storage tanks and surface water releases of 

petroleum fuels. Statistical analysis of gasoline samples, however, is not a sufficient 

basis for understanding variations in gasoline composition across the United States. 

Familiarity with the United States’ unique regulatory requirements is a necessary 

precursor to studying gasoline composition. This report gives an overview of the 

regulations affecting major contaminants at leaking underground storage tank sites. 

Candida C. West, Ph.D. 

Acting Director 

Ecosystems Research Division 

Athens, Georgia 

4
Leaking Underground Storage Tank Assessment Report 

Series 

A series of research reports is planned that will present data and models for leaking 

underground storage tank risk assessments. To date, these include: 

1. Gasoline Composition

Weaver, James W., Linda R. Exum, Lourdes M. Prieto, 2008, Gasoline Composition 

 Regulations Affecting LUST Sites, United States Environmental Protection 

 Agency, Washington, D.C., EPA/600/R-10/001. 

Weaver, James W., Sheldon A. Skaggs, David L. Spidle, and Guthrie C. Stone, 2009, 

 Composition and Behavior of Fuel Ethanol, United States Environmental 

 Protection Agency, Washington, D.C., EPA/600/R-09/037. 

Weaver, James W., Lewis Jordan and Daniel B. Hall, 2005, Predicted Ground Water, Soil 

 and Soil Gas Impacts from US Gasolines, 2004: First Analysis of the Autumnal 

 Data, United States Environmental Protection Agency, Washington, D.C., 

 EPA/600/R-05/032. 

2. Simulation Models

Gorokhovski, Vikenti M. and James W. Weaver, 2007, A Catalog of Ground Water Flow 

 Solutions for Plume Diving Calculations, United States Environmental Protection 

 Agency, Washington, D.C. 

Weaver, James W., 2004, On-line Tools for Assessing Petroleum Releases, United States 

Environmental Protection Agency, Washington, D.C., EPA 600/R-04/101. 

3. Model Background and Evaluation 

Weaver, James W. and C. S. Sosik, 2007, Assessment of Modeling Reports for Petroleum 

Release and Brownfields Sites, United States Environmental Protection Agency, 

Washington, D.C., EPA 600/R-07/101. 

As reports are added to this series, they can be found on EPA’s web site: 

http://www.epa.gov/athens/publications. 

5
Contents 

Notice.................................................................................................................................. 2 

Abstract............................................................................................................................... 3 

Foreword............................................................................................................................. 4 

Leaking Underground Storage Tank Assessment Report Series ........................................ 5 

Contents .............................................................................................................................. 6 

Introduction......................................................................................................................... 7 

Regulatory History.............................................................................................................. 7 

Data Sources ..................................................................................................................... 10 

Reformulated and Conventional Gasoline........................................................................ 15 

Reformulated Gasoline ................................................................................................. 15 

State Cleaner Burning Gasoline Programs ................................................................... 17 

Conventional Gasoline.................................................................................................. 17 

Geographic Extent ........................................................................................................ 18 

Oxygenated Gasoline........................................................................................................ 21 

MTBE Bans ...................................................................................................................... 26 

Discussion and Conclusions ............................................................................................. 29 

References......................................................................................................................... 31 

Acknowledgments............................................................................................................. 37 

6
Introduction 

The magnitude of environmental contamination from gasoline releases depends, 

among other factors, on composition of the gasoline. The amount of certain components 

in gasoline varies for a number of reasons, including fuel performance characteristics, 

refinery equipment and capabilities, crude oil sources, industry standards and regulation. 

Of the many causes of variability, regulatory requirements may be dominant for some 

components. Limits on certain component concentrations and properties have been set 

by regulation. Benzene, ethers and alcohols are the best examples of components with 

limitations, and vapor pressure is the best example of a limited property. In addition to 

being regulated for their impact on air pollution, benzene and methyl tert-butyl ether 

(MTBE) and other oxygenates are ground water contaminants. This report gives an 

overview of the air quality regulations that affect major contaminants at leaking 

underground storage tank sites.1

History 

The Clean Air Act of 1970 established the framework for setting nation-wide air 

quality goals (NAAQs) for pollutants Subsequently, states developed implementation 

plans (SIPs) to meet those goals. To date, the U.S. Environmental Protection Agency 

(EPA) and states have set goals for six pollutants: sulfur dioxide, particulate matter, 

nitrogen oxides, carbon monoxide (CO), ozone, and lead (Ayres and Kornreich, 2004). 

EPA was authorized to require registration and testing of specified fuels and fuel 

additives (US Federal Register, 1975, 1976). Because of these requirements, we know 

MTBE was registered for use in 1979, tert-amyl methyl ether (TAME) in 1981, and ethyl 

tert-butyl ether (ETBE) in 1981 (Stikkers, 2002). Under authority granted by the Clean 

 

1

 The information provided in this paper is not intended for determining compliance with 

state or federal regulations for air quality, gasoline composition or other similar purposes. 

For these purposes, information should be obtained from the appropriate local, state and 

federal regulatory agencies, the Clean Air Act, the United States Code, the Code of 

Federal Regulations, the Federal Register and other sources. 

7
Air Act, EPA began to phase out leaded gasoline over a period of time that ended on 

January 1, 1996. The original focus of the Clean Air Act was to limit emissions through 

improved vehicle technology. As time went on this approach became less viable for 

solving persistent pollution problems, and Congress believed that lead was being replaced 

by toxic organic chemicals (Martels, 2004). Consequently, the Clean Air Act 

Amendments (CAAA) of 1990 (42 U.S. Code 4701) expanded regulation of fuels to help 

meet NAAQs for ozone and carbon monoxide and reduce toxic air pollutants (e.g., 

benzene). 

The CAAA introduced several requirements that have had a major impact on 

gasoline composition throughout the United States, beginning with implementation in 

1992 and 1995, and continuing to the present. The most important requirements for 

LUST sites were the total ban on lead in gasoline, and new requirements for three types 

of gasoline: conventional, reformulated, and oxygenated. Both reformulated gasoline 

(RFG) and oxygenated gasoline (OG) required oxygen-containing additives, because the 

fuel would burn cleaner. Initially, the most common oxygenate was MTBE. The RFG 

program limited the amount of benzene and total aromatics in reformulated gasoline. 

Since RFG areas were specified at county or partial-county level or, in a few cases, at the 

city level, there are different requirements in adjoining counties. This spatial distinction 

between RFG and CG might not be absolute, however, because market forces guide 

gasoline sales, and there are no restrictions on selling RFG in CG counties. 

Parts of the country not using RFG were also affected by the CAAA because the 

Act contained an anti-dumping provision to prevent air quality deterioration in areas 

using conventional gasoline (CG). This requirement prevented benzene from being 

moved out of the RFG and into the CG supply by establishing benzene concentration 

limitations from producer/importer baseline conditions that existed in 1990. An 

important distinction between CG and RFG is that CG baseline limitations are applied to 

producers/importers, while RFG requirements apply to where the fuel is used. 

8
Consequently, at a given location the benzene concentration in CG is usually variable and 

not very predictable2. 

 In response to dissatisfaction with ground water contamination, a number of state 

legislatures banned MTBE and, in some cases, other ethers and alcohols, beginning in 

2000. These state bans did not affect federal oxygen requirements for RFG and OG, 

however, so MTBE typically was replaced by ethanol. In 2005, Congress passed the 

Energy Policy Act (EPAct 2005) which removed the oxygenate mandate from the RFG 

program. Gasoline suppliers responded by reducing the use of MTBE and other ethers. 

A composition-related aspect of gasoline is octane number. Some gasoline -- 

called straight run gasoline -- is a direct output from distilling crude oil, but its octane 

number is too low to prevent engine knock in modern engines. Therefore, the octane 

number is boosted in a number of ways. These commonly include the use of alkyl leads, 

aromatic hydrocarbons, ethers, alkylate and alcohols (Owen and Coley, 1995). Shifts 

among these have occurred, partly due to laws and regulations that address different goals 

(see e.g., Stikkers, 2002). Only small amounts of certain additives, 1 g/L or less of alkyl 

leads or 0.017 g/L methylcyclopentadienyl manganese tricarbonyl (MMT), are needed to 

increase octane levels from 5 to 25 octane numbers, depending on the blendstock (Owen 

and Coley, 1995). Blending higher amounts of some organic compounds also increases 

resistance to engine knock, but their levels typically must be one percent or higher. In 

1979, MTBE was registered as an octane enhancer, so it may have appeared in gasoline 

for octane purposes even when there was no regulatory mandate for oxygenated 

additives. This has been borne out by gasoline composition studies in which MTBE 

appeared in CG when it was not required (Weaver et al., 2005). 

Timing of the mandates varied according to federal requirements or state 

implementation plans. Nationally, the RFG program had an implementation date of 

January 1, 1995, so RFG began appearing on the market in late 1994. Opt-out and opt-in 

 

2

 In 2011 the Mobile Sources Air Toxics rule (U. S. Federal Register, 2007) will reduce benzene levels in 

all gasoline. 

9
provisions allowed areas to enter or leave the programs at different times. The 

oxygenated gasoline program began in the fall of 1992. Since it specified oxygenated 

fuel to be used only during a few months in winter, there was a characteristic pattern of 

oxygenate usage in these locations. Where NAAQs for CO were met later, 

implementation plans were revised to remove oxygenated gasoline requirements; for 

example, see U. S. Federal Register (1999, 2000) for an example from New York State. 

Data Sources 

In the next two sections, data from three sources were compared to the regulatory 

time lines. First was the Northrup-Grumman data set (e.g., Dickson, 2006), which 

published results from an industry consortium that has collected data since the 1930s. 

This company is the latest successor to the well-known National Institute for Petroleum 

and Energy Research (NIPER). Its analyses were performed using ASTM standard 

methods for analysis of aromatics, ethers and alcohols. Northrup-Grumman data from 

1976-2007 were obtained in an electronic format, then sorted by city and octane number 

(ON). Three octane number classes were used: regular (less than 88.5 ON), mid-grade 

(88.5 ON to 90 ON), and premium (above 90 ON). 

The second source was data from the Reformulated Gasoline Survey Association. 

This group conducts surveys of RFG required by the Clean Air Act and reports the results 

to EPA, which then evaluates the data for compliance. California is not included in these 

surveys. 

Lastly, the U.S. Department of Energy’s Energy Information Agency (EIA) 

collects weekly data from producers on their production of gasoline and a variety of fuel 

components. 

Leaded Gasoline 

Use of lead in gasoline declined throughout the 1980s (Figure 1) and this phasing 

out contributed to the rise in use of ether in gasoline (Stikkers, 2002). Averaged data 

10
from NIPER/Northrup-Grumman show that lead usage was highest in premium gasoline 

and, on average, lower in mid-grade and regular gasoline. For example, Figure 1 shows 

that in 1978, premium gasoline contained at least 1 g/gal, mid-grade at least 0.5 g/gal, 

and regular may have contained no lead at all. After reaching levels as high as 4 

g/gallon, by 1986 most lead was reduced to concentrations of 1 g/gallon. Complete 

removal of lead was mandated by the Clean Air Act Amendments of 1990, and occurred 

on January 1, 1996. Lead can still be used, however, in aviation gasoline and racing 

fuel. 

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998

0

1

2

3

4

5

Lead (g/gal)

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998

0

1

2

3

4

5

Lead (g/gal)

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998

Year

0

1

2

3

4

5

Lead (g/gal)

Premium (>90 Octane)

Mid Grade (88.5 < Octane < 90)

Regular (<88.5 Octane)

Figure 1 Data illustrating the phasing out of lead from gasoline in the United States in premium 

(top), mid-grade (middle), and regular (bottom). After declining through the 1980s, lead was 

completely eliminated by January 1, 1996 by the Clean Air Act Amendments of 1990. 

11
Gasoline Production in the United States

Gasoline production data compiled by EIA document the production of 

conventional and reformulated gasoline. The data show that production of RFG began in 

September 1994, shortly before the RFG program was implemented when RFG replaced 

part of total gasoline production in the U.S. (Figure 2 A). The remainder of production 

became conventional gasoline (see U.S. CFR, 2007, Title 40, Part 80, Section 2). 

Production of both types of gasoline tended to increase over time. In 2004, EIA began 

differentiating ether-, alcohol-, and non-oxygenated RFG (Figure 2 B). The data show 

declining use of ether in RFG from 2004 until mid-2006, when ethers finally were 

replaced by alcohol. The slow decline of ether use corresponds to when MTBE was 

being banned by the states. When the oxygenate mandate was removed by the Energy 

Policy Act of 2005, ethers were removed from RFG. While ether use was declining, 

alcohol use was increasing until almost all RFG produced after the EPAct 2005 took 

effect contained alcohol. This legislation also required increased use of ethanol, as 

shown by the increased amount of all gasoline containing ethanol. By December 2009, 

77% of all U.S. gasoline contained alcohol. 

 RFG Survey Association data indicate that MTBE in RFG outside California 

decreased, on average, from 7.9% to 0.01%; ethanol increased from 2.2% to 9.2%; and 

benzene remained nearly the same -- 0.61% in 2002 versus 0.69% in 2006. These data 

also document removal of ethers from the U.S gasoline supply (Figure 4). Ether levels 

in gasoline declined throughout the summer months of 2006, so that the date when the 

oxygenate requirement was removed did not correspond to immediate removal of ethers. 

Some U.S. gasoline is imported, but no RFG with ether has been imported since June 

20063

 (Figure 3 A). Production of RFG with ether has continued sporadically at very 

low levels from 2004 through 2009 (Figure 3 B)4

. 

 

3

 Conventional gasoline is also imported, but EIA data show only very small amounts of alcohol-containing 

gasoline has been imported, and none since Mar, 2008. 

4

 EIA export data show only the total of petroleum products exported. 

12
 

1982

19841986198819901992199419961998200020022004200620082010

Year

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Thousand Barrels 

Per Day

20052006200720082009

Year

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000 Total

Conventional

Reformulated

Total

CG and RFG

with alcohol

RFG with alcohol

RFG with ether

A B

Figure 2 DOE gasoline production data. A. Prior to the Clean Air Act Amendments, there was no 

distinction between conventional and reformulated gasoline. Since 1995, the proportion of 

conventional gasoline has remained roughly constant. B. Since removal of the oxygenate mandate in 

2006, the amount of reformulated gasoline with ether has declined dramatically, although there has 

been a commensurate increase in RFG with alcohol. Mandates for increased use of ethanol have 

increased the amount of CG with alcohol, while the amount of RFG with alcohol has remained 

roughly constant. The total amount of gasoline with alcohol has increased to be approximately 77% 

of the total in December 2009. 1981 1983 1985 1987 1989 1991

199319951997199920012003200520072009

2011

Year

0

200

400

600

800

1000

1200

1400

1600

1800

Thousand Barrels

per Day

Total Imported

Gasoline

Imported RFG 

with Ether

2007200820092010

Year

0

10

20

30

40

50

Thousand Barrels

Per Day

A B

U.S. Produced

RFG with Ether

Figure 3 A. Gasoline imported into the U.S. from 1982 to 2009. Some RFG with ether was 

imported prior to 2006, but none since. B. From 2006 to 2009, small amounts of RFG with ether 

have been produced in the U.S. 

13
0

5

10

15

MTBE (Vol %)

Feb-06Mar-06

Apr-06

May-06

Jun-06

Jul-06

Aug-06Sep-06

Oct-06

Nov-06

Dec-06

Jan-07

Date

0

5

10

15

ETBE (Vol %)

0

5

10

15

TAME (Vol %)

0

5

10

15

DIPE (Vol %)

Figure 4 RFG Survey Association data, as reported to EPA, show that the removal of ethers from 

reformulated gasoline (except in California) occurred over the summer months of 2006. 

14
Reformulated and Conventional Gasoline 

Reformulated Gasoline 

EPA defines reformulated gasoline as gasoline that is certified (U.S. CFR, 2007, 

Title 40, Part 80, Section 41) to meet requirements and standards specified in U.S CFR, 

2007, Title 40, Part 80, Section 42. The requirements varied during four time periods: 

1995-1997; 1998-1999; 2000 to May 5, 2006; and May 5, 2006 to the present (April 24, 

2006 in California, see U.S. EPA, 2006). Although other requirements of RFG changed 

over these times, the required oxygen content and benzene limitation did not change until 

the Energy Policy Act passed in 2005 (Table 1). The oxygen requirement was removed 

in California effective April 24, 2006, and in the rest of the U.S. effective May 5, 2006. 

Beginning in 2011, benzene content in all U.S. gasoline will be reduced to 0.62 vol % to 

comply with the Mobile Sources Air Toxics Rule (U.S. Federal Register, 2007). 

As shown in Table 1, standards were met on either an averaged or per-gallon 

basis. Using average basis, oxygen concentration in a gallon may have been as low as 

1.5 wt %, but had to average 2.1 wt %. The total oxygen content could have been limited 

to 3.2 wt % when gasoline contained ethanol (U.S. CFR, 2007, Title 40, Part 80, Section 

41 (g)(i)). 

Table 1 Oxygen and benzene requirements for reformulated gasoline. 

RFG Content Requirements 

Averaged Basis 

Component Effective Dates 

Per-gallon 

Basis Standard Limit 

Oxygen (weight percent) 1995 to May 5, 2005  2.0  2.1  1.5 

May 5, 2005 to present none none none 

Benzene (volume percent) 1995 to present  1.00  0.95  1.30 

The amounts of various ethers and ethanol that were needed to meet the oxygen 

requirement are shown in Table 2; for example, a gallon of gasoline containing 11.0 vol 

% MTBE met the per gallon oxygen requirement of 2.0 wt %. If the producers chose to 

15
meet the standard on an averaged basis, there could have been compliant gasoline with 

MTBE content as low as 8.25 vol %. Thus, while a gallon of gasoline containing 11.0 

vol % MTBE clearly complied with the standard, gasoline containing less than 11.0 vol 

% could comply in two ways. First, if the producer chose to meet the standard on an 

average basis and the batch met the 2.1 wt % oxygen requirement, then the fuel was 

compliant. The second was when more than one oxygenate was present: any single 

oxygenate could be present in a relatively low concentration, but the total oxygen 

supplied by all compounds had to meet the requirement. Similarly, RFG containing 1.0 

vol% benzene complied with the per-gallon basis. One specific gallon of gasoline 

containing 1.30 vol % benzene could be compliant if the producer met the standard using 

the average basis. 

Table 2 Oxygen and required amounts of oxygenates to meet requirements of reformulated and 

winter oxygenated gasoline. Values given as weight percent. 

Required Oxygenate Concentration 

RFG Winter Oxygenate 

Averaged Basis 

 

Per-gallon 

Basis Standard Minimum 

Weight percent of oxygen 2.0 % 2.1% 1.5% 

2.7% 

oxygen 

required 

3.1% oxygen 

required 

Common Oxygenates and Required Content to Meet Oxygen Requirements 

Methyl tert-butyl ether 11.0% 11.6% 8.25% 14.9% 17.1% 

Ethyl tert-butyl ether 12.75% 13.4% 9.6% 17.2% 19.8% 

Tert-amyl methyl ether 12.75% 13.4% 9.6% 17.2% 19.8% 

Diisopropyl ether 12.75% 13.4% 9.6% 17.2% 19.8% 

Ethanol 5.8% 6.0% 4.3% 5.4% 6.2% 

16
State Cleaner Burning Gasoline Programs 

Three states, Arizona, California and Nevada, have implemented cleaner burning 

gasoline (CBG) programs. A summary of requirements for California’s program are 

given in Table 3. Arizona requires cleaner burning gasoline in the Phoenix area (U.S. 

Federal Register, 2004), and Nevada requires the same for the Las Vegas area (Clark 

County, Nevada, 2003). Arizona’s cleaner burning gasoline matches the characteristics 

of either federal RFG or California CBG. Nevada imposes limits on sulfur and aromatic 

composition. 

Table 3 MTBE and benzene requirements for California cleaner burning gasoline (CBG), given in 

units of volume %. California allows refiners to meet standards for each batch of finished gasoline—

the “flat” limit. Alternatively, a refiner can meet standards on an average over 180 days. In the 

latter case, the averaging limit must be met for all batches and no batch can exceed an upper/lower 

limit (“cap”). The lower cap limit of 1.8% in Phase 2 and Phase 3 apply to certain counties in the 

winter (California, 2003a). 

Phase 1 Phase 2 Phase 3 

January, 1992 March, 1996 January, 2004 

flat avg cap flat avg cap 

Oxygen content 1.8%-2.3% 1.8% – 2.2% n/a 1.8%-3.5% 

0% – 3.5% 

1.8% – 2.2% n/a 1.8%-3.5% 

0 %– 3.5% 

Benzene 1.7% 1.0% 0.80% 1.20% 0.80% 0.70% 1.10% 

Conventional Gasoline 

Conventional gasoline is gasoline that has not been certified as RFG (i.e., meeting 

the U.S. CFR, 2007, Title 40, Part 80, Section 41 requirements), but it must meet 

requirements of anti-dumping provisions of the CAAA (U.S. CFR, 2007, Title 40, Part 

80, Section 90 and following sections). These were designed to prevent increased 

average per-gallon emissions of volatile organic compounds, nitrogen oxides, carbon 

monoxide and toxic air pollutants, in addition to requirements imposed on reformulated 

gasoline (CAAA Sec 211(k)(8)). Baselines for each refiner and producer were set, using 

their production/importation for 1990, or by statutory baseline with a benzene content of 

1.53 vol % for winter and 1.64 vol % for summer (U.S. CFR, 2007, Title 40, Part 80, 

Section 91(c)(5) and Section 45, (b)(2)). Other features of the statutory baseline are 

17
given in Table 4. Because of different producer baselines, benzene content of gasoline in 

conventional gasoline areas can vary. Recent EPA studies have shown benzene content 

in conventional gasoline ranged from 0.5 vol % to 3.0 vol % or in very limited instances 

to 5% (Weaver et al., 2005).. 

Table 4 Selected parameters of the statutory baseline for conventional gasoline (40 CFR 80.91 and 

40 CFR 80.45) 

Parameter Winter 

40CFR 80.91(c)(5)(i) 

40CFR 80.45(b)(2)

Summer 

40CFR 80.91(c)(5)(ii) 

40CFR 80.45(b)(2)

Average 

40CFR 80.91(c)(5)(ii) 

Benzene (vol %) 1.64 1.53 1.60 

Aromatics (vol %) 26.4 32 28.6 

Olefins(*) (vol %) 11.9 9.2 10.8 

Reid Vapor Pressure 

(psi) 

8.7 8.7 8.7 

API Gravity(**) (o

API) 60.2 57.4 59.1 

(*)Olefins are also known as alkenes 

(**) API Gravity (o

API) is defined by: 

5.131 5.141   SpecificGravity GravityAPI

Geographic Extent 

A map of locations required to use federal reformulated and conventional gasoline 

is shown in Figure 5. The map shows that RFG has been used in the northeast corridor, 

large Midwestern cities, Arizona and California. It also shows that geographically, most 

of the U.S. uses conventional gasoline. For the majority of counties using RFG, the RFG 

oxygenate mandate was in force from January 1, 1995 to May 5, 2006. Counties in the 

Los Angeles area were included at the beginning of the program, but had an earlier date 

(April 24, 2006) for removing the oxygen mandate. Counties in the Sacramento 

metropolitan area were added in 1996, and those in the San Joaquin Valley in 2002. 

These latter two groups also share the April 2006 federal oxygen mandate removal date. 

18
19

Counties in the St. Louis, Missouri metropolitan area opted into the program on 

June 1, 1999. Four counties in Illinois opted into the RFG program in 2007 and, because 

of the late date, never were required to use oxygenates. In 1997, the Phoenix 

metropolitan area opted into the program, then opted out in 1998 because of Arizona’s 

cleaner-burning gasoline program (see Figure 5 and U.S Federal Register, 2004). Seven 

counties in Maine opted out of the program in 1999. 
Fe deral Oxygenate Re quirement Duration

1.1.95 to 3.10.991.1.95 to 4.24.061.1.95 to 5.5.0 66.1.96 to 4.24.068.1.97 to 6.18.986.1.99 to 5.5.0 612.10 .02 to 4.24.06NoneState Cle aner Burning Gasoline (CBG)

0 200 400 600 800 1000 Kim

Figure 5 Federal reformulated gasoline and state cleaner-burning gasoline programs in the United States (California, 2003a; C

2003; U.S. CFR, 2005, Title 40, Part 80, Section 40 U.S. CFR, 2007, Title 40, Part 80, Section 40, U.S Federal Register, 2004). D

mandates are shown on the legend. All areas not highlighted on the map use conventional gasoline. Reformulated gasoline is r

elevation on Whiteface Mountain in northern New York. 
Oxygenated Gasoline 

The Clean Air Act Amendments (42 U.S.C. 7545, m, 1) required states to 

mandate at least 2.7 wt % oxygen in gasoline sold in areas where carbon monoxide 

standards were not attained. This requirement was imposed for at least four months of 

the year when ambient CO concentrations were highest. EPA could reduce the duration 

if a state demonstrated there were no exceedances of the carbon monoxide standard. If a 

carbon monoxide standard was not attained by a required date, gasoline containing 3.1% 

by weight was required. 

The areas were defined as the larger of Consolidated Metropolitan Statistical 

Area or Metropolitan Statistical Area. The program began in late fall 1992 in 39 areas, 

with one more added in 1993. Six cities began winter oxygenate programs earlier -- in 

the 1989/1990 winter season: Denver, Colorado; Reno and Las Vegas, Nevada; Tucson 

and Phoenix, Arizona; and Albuquerque, New Mexico (Stikkers, 2001). Table 5 lists the 

nine areas still in the program to the present, along with their required oxygen content 

and effective months. Table 6 lists areas that no longer implement the program, and their 

effective ending dates. The geographic concentration of remaining cities in the southwest 

is shown in Figure 6. Table 7 lists cities that have exited the program, but retain the 

option of using oxygenated gasoline as a contingency measure. 

Six states have state-wide oxygenate mandates (Table 8). Each of the state 

requirements differ, but the required ethanol contents do not exceed the federal limit of 

10%. Montana imposed a conditional requirement for using ethanol in gasoline, in 

conjunction with a conditional ban on MTBE (Montana, 2005) that has so far not been 

imposed (Kuhn, 2010). 

21
Table 5 Cities currently implementing the winter oxygenates program (U.S EPA, 2008c). 

Control Period Area (Consolidated Metropolitan Statistical Area) Oxygen Content (wt %) 

10/1 to 1/31 Reno, NV 3.5 

10/1 to 3/31 El Paso, TX 2.7 

Las Vegas, NV 3.5 

Reno, NV 3.5 

Tucson , AZ 1.8 

11/1 to 2/29 Albuquerque, NM 2.7 

Missoula, MT 2.7 

Los Angeles, CA 1.8 to 2.2 

11/2 to 3/31 Phoenix, AZ 3.5 

22
23

Table 6 Cities exiting the winter oxygenates program (U.S. EPA, 2008c). 

Area (Consolidated Metropolitan Statistical 

Area) 

Effective Exit Date 

Syracuse, NY Sep 29, 1993 

Cleveland, OH Mar 7, 1994 

Greensboro, NC Nov 7, 1994 

Duluth, MN Jun 13, 1994 

Memphis, TN Sep 26, 1994 

Raleigh-Durham, NC Sep 18, 1995 

Baltimore, MD Dec 15, 1995 

Hartford, CT Jan 2, 1996 

Philadelphia, PA Mar 15, 1996 

Washington, DC Mar 15, 1996 

Boston, MA Apr 1, 1996 

Seattle, WA Oct 11, 1996 

Vancouver, WA Oct 21, 1996 

San Diego, Chico, Modesto, Sacramento, 

Fresno, San Francisco, and 

Stockton, CA 

Jun 1, 1998 

New Haven, CT Dec 4, 1998 

Salt Lake City, UT Mar 22, 1999 

Northern NJ/ 

Southwest CT/ 

New York, NY 

Nov 22, 1999 

Jan 31, 2000 

May 19, 2000 

Minneapolis/St. Paul, MN Nov 29, 1999 

Colorado Springs, CO Feb 20, 2000 

Ogden, UT May 8, 2001 

Ft. Collins, CO Jan 1, 2004 

Provo/Orem UT Jan 3, 2006 

Portland, OR Feb 23, 2006 

Denver/Boulder, CO Oct 16, 2007 

Longmont, CO Oct 16, 2007 

Table 7 Cities exiting the winter oxygenates program (U.S. EPA, 2008c), with oxygenated gasoline as 

a contingency measure in their states’ maintenance plans. 

Area (Consolidated Metropolitan Statistical Area) Redesignation/SIP Change Published in the 

Federal Register 

Grants Pass, OR Oct 30, 2000 

Klamath Co, OR Nov 19, 2001 

Medford, OR Sep 23, 2002 

Anchorage, AK Jul 23, 2004 

Spokane, WA Aug 29, 2005 
Table 8 State ethanol mandates. 

State Ethanol 

Requirement 

Vol % 

Effective Date Citation 

Florida 9 to 10 Dec 21, 2010 Florida, 2009 

Hawaii 10 1994 Hawaii, 2004 

2.7 (a) Oct 1, 1997 Minnesota, 1997 

9.2 to 10 2003 Minnesota, 2003 

Minnesota 

 

20 or max allowed 

by EPA 

Aug 20, 2013 Minnesota, 2009 

Missouri 10 Jan 1, 2008 Missouri, 2008 

Oregon 10 Nov 1, 2009 Oregon, 2009 

Washington “2% of gasoline” Dec 1, 2008 Washington, 2009 

(a)Oxygenated fuel requirement, Minnesota ethanol producer credit caused ethanol usage. 

24
Figure 6 Oxygenated gasoline programs in the United States. Cities where an oxygenated additive was, or is, required for win

indicated by triangles and circles, respectively. Six states have imposed year-round oxygenate mandates. Montana has a future 

conditional on in-state ethanol production. 
MTBE Bans 

Twenty-six states, two counties, and one city have banned MTBE in gasoline 

(Figure 7). Three states have imposed absolute bans, while most allow some MTBE to 

remain in gasoline (Table 9). In 17 states, the level was 0.5%, but ranged from 0.05% in 

California to 1% in Nebraska. Six states banned MTBE and other oxygenates which 

included the other gasoline oxygenate ethers: ethyl tert-butyl ether (ETBE); tert-amyl 

methyl ether (TAME); diisopropyl ether (DIPE); and alcohols, mostly tert-butyl alcohol 

(TBA). The bans did not affect requirements to use reformulated or oxygenated-gasoline, 

but did cause a shift to another oxygenate. One data set shows that the other oxygenate 

most commonly used was ethanol (Weaver et al., 2005). Oregon passed a conditional 

ban of various ethers and alcohols, but was only effective if these were banned by each of 

the California Air Resources Board, the California Environmental Policy Council and the 

US EPA (Oregon, 2009).

26
#

Pacific

Ocean

Gulf of Mexico

Arizona

2005

North Carolina

01/08

Washoe

County NV

12/03

California

12/03

El Dorado

County CA

04/2000

01/04

Washington

Colorado

04/02

North Dakota

08/05

South Dakota

07/01

Nebraska

07/00

Kansas

07/04

Minnesota

07/00

Wisconsin

08/04

Iowa

12/00

Missouri

07/05

Michigan

06/03

Ohio

07/05

01/04

New York

01/06

Kentucky

Main

01/0

Indiana

Illinois 07/04

07/04

Chicago

12/00

Total MTBE ban or notgreater than

0.05 vol%0.3 vol%0.5 vol%0.6 vol%1.0 vol%Total MTBE banTrace amounts onlyNo ban

Ha

Rhod

0

Connecti

New Jerse

Atlantic

Ocean

Alaska

not to scale Hawaii

Figure 7 State MTBE, ether, and/or alcohol bans, showing effective dates and maximum levels allowed for MTBE. Please r

details on other ethers and alcohols.
Table 9 MTBE and other oxygenate ban dates, maximum allowable limits, and citation. 

State/County/City Ban Dates de minimis Levels (vol%) Citations 

Enacted Effective MTBE ETBE TAME DIPE TBA Others 

Arizona 05/11/04 01/01/05 0.3 * * * * * Arizona (2004) 

12/31/03 0.60 **   **  ** 

07/01/04 0.30   **  ** ** 

12/31/05 0.15 California 03/14/03 

07/01/07 0.05 

California Air 

Resources Board 

(2003b) 

Chicago 12/13/00 12/13/00 none City of Chicago (2000) 

Colorado 09/01/00 04/30/02 none Colorado (2000) 

Connecticut 06/18/03 01/01/04 0.5 Connecticut (2003) 

El Dorado 

County, California 03/28/00 4/28/00 none El Dorado County (2000) 

Illinois 07/24/01 07/24/04 0.5 Illinois (2001) 

Indiana 07/01/02 07/23/04 0.5 Indiana (2002) 

Iowa 07/01/00 12/31/00 0.5 Iowa (2000) 

Kansas 07/01/01 07/01/04 0.5 Kansas (2004) 

Kentucky 07/15/02 01/01/06 0.5 Kentucky (2002) 

Maine 07/30/05 01/01/07 0.5 Maine (2005) 

Michigan 06/26/00 06/01/03 ☼ Michigan (2000) 

07/01/00 0.33 0.33 0.33 Minnesota 04/20/00 

07/01/05 none none none 

Minnesota (2000) 

Missouri 08/28/02 07/01/05 0.5 Missouri (2002) 

Nebraska 04/11/00 07/13/00 1.0 Nebraska (2000) 

New Hampshire 05/27/04 01/01/07● 0.5 ▲ ▲ ▲ 0.5 0.5 New Hampshire (2004) 

New Jersey 08/18/05 01/01/09 0.5 New Jersey (2005) 

New York 05/24/00 01/01/04 0.5 New York (2000) 

North Carolina 06/21/05 01/01/08 0.5 North Carolina (2005) 

North Dakota 03/31/05 08/01/05 0.5 North Dakota (2005) 

Ohio 08/28/02 07/01/05 0.5 Ohio (2002) 

Rhode Island 07/06/05 06/01/07 0.5 0.5 0.5 0.5 ◘ ◘ Rhode Island ( 2005) 

02/16/00 07/01/00 2.0 South Dakota 

02/28/01 07/01/01 0.5 

South Dakota (2000) 

Vermont 05/23/05 01/01/07 0.5 0.5 0.5 0.5 Vermont (2005) 

Washington 05/09/01 01/01/04 0.6 Washington (2001) 

10/25/00 12/31/03 

10/1–1/31 0.30 Washoe County, 

Nevada Revised 

09/22/05 

09/22/05 

Yr round 0.30 

Washoe County District 

Board of Health (2005) 

Wisconsin 08/11/03 08/01/04 0.5 Wisconsin (2003) 

*Sum of diisopropylether (DIPE), ethyl tert-butylether (ETBE), isobutanol, isopropanol, methanol, n-butanol, n-propanol, sec-butanol, tert-amylmethylether 

(TAME), tert-butanol, tert-pentanol (tert-amylalcohol) not to exceed 0.1% by volume, starting 01/01/2006 

**Sum of methanol, isopropanol, n-propanol, n-butanol, isobutanol, sec-butanol, tert-butanol tert-pentanol (tert-amylalcohol), ethyl tert-butylether (ETBE), 

diisopropylether (DIPE), tert-amylmethylether (TAME) not to exceed 0.10 weight % oxygen, starting 12/31/2003, sum of same not to exceed 0.06 weight % 

oxygen, starting 07/01/2004 

♦"”...within 12 months after the Department of Transportation has certified that the State of Montana has produced 40 million gallons of denatured ethanol and 

has maintained that level of production on an annualized basis for at least 3 months...ensure that all gasoline sold to consumers ....may not contain more than 

trace amounts of the additive methyl tertiary butyl ether.” Montana Code Annotated 2005 82-15-121 

●”...shall take effect on the later of 01/01/07 or 6 months after federal approval” to opt out of the Federal Reformulated Gasoline Program (see paragraph II, 

Section 1 of Act 175-4) 

▲”No person...shall sell...any neat gasoline ethers or gasoline containing MTBE, other gasoline ethers or tertiary butyl alcohol (TBA) in quantities greater 

than 1⁄2 of 1% by volume” 

◘ Other ether oxygenates not greater than 0.5%: methanol, isopropanol, n-propanol, n-butanol, sec-butanol, tert-butanol, tert-pentanol (tert amylalcohol) 

isobutanol

28
Discussion and Conclusions 

The Clean Air Act Amendments of 1990 imposed a set of requirements for gasoline in 

the United States. For LUST sites, the three most important are: 

1) Final Ban of Leaded Gasoline 

Banning leaded gasoline had two major effects on LUST sites. First, 

removing lead resulted in new ways to boost the octane rating of gasoline. Most 

significant was the introduction of MTBE and other ethers, beginning in 1979; 

notably, this predates oxygenate requirements of the Clean Air Act Amendments. 

Second was the concurrent removal of lead scavengers. These compounds – 

ethylene dibromide and 1,2 dichlorethane – prevent precipitation of lead on 

engine parts. They recently were shown to persist in ground water at some sites 

(Falta, 2004, Falta et al., 2005), and continue to cause contamination problems. 

2) Conventional and Reformulated Gasoline 

The Clean Air Act Amendments of 1990 created a framework for the two 

major types of gasoline sold in the U.S., reformulated and conventional. With a 

few exceptions, use of RFG has been on a county-by-county basis. Although 

most of these locations have used RFG for long periods, some changes have 

occurred as indicated on Figure 5. 

The composition of RFG is specified by provisions of the Clean Air Act. 

Relevant for leaking underground storage tanks are provisions that limit benzene 

to a nominal level of 1.0% by volume and, until mid-spring of 2006, required an 

oxygenated additive at 2.0% by weight. Conventional gasoline is gasoline which 

is not reformulated -- the remaining gasoline in the U.S. The benzene content in 

conventional gasoline is limited by producer/importer baselines set in 1990. 

Because the baselines are not tied to point-of-use, they do not provide a guide for 

specific locations. Another complicating factor is the use of oxygenates as octane 

29
enhancers. These could be used anywhere and evidence of their preferred use in 

premium gasoline appears in a companion study. 

3) Oxygenated Gasoline Program 

The Clean Air Act Amendments of 1990 mandated states to require 

oxygenated gasoline in areas that did not attain carbon monoxide standards in the 

winter months. Beginning in 1992, these requirements were imposed in selected 

cities, but as carbon monoxide standards were met, cities gradually dropped out of 

the program. 

The CAAA of 1990 indirectly led to a fourth impact on gasoline composition, which 

occurred because of the states’ reaction to ground water contamination by MTBE: 

4) State MTBE and Other Oxygenate Bans 

Beginning in 2000, state legislatures enacted bans or restrictions on 

oxygenate usage in gasoline. In some cases these included only MTBE, while in 

others a whole suite of ethers and alcohols were restricted. Most restrictions 

allowed MTBE content of up to 0.5% by volume. There continues to be sporadic 

production of small amounts of RFG with ether, which could be used in states 

without ether bans. 

Despite changes caused by the states’ oxygenate limitations and by removal of the 

oxygenate mandate for reformulated gasoline, the framework for reformulated and 

conventional gasoline is still in place in the United States. State oxygenated gasoline 

programs, mostly in the southwestern United States, continue to rely on ethanol to meet 

their oxygenate requirements. Ethanol usage has increased steadily so that 77% of U.S. 

gasoline now contains ethanol. Benzene concentrations in RFG were limited to 1 vol %, 

and will be further reduced to 0.62 vol % in all U.S. gasoline by 2011. 

30
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36
37

Acknowledgments 

The authors appreciate the assistance of Kurt Gustafson, of the US EPA, Office of 

Transportation and Air Quality, Tim Hogan of the National Petrochemical and Refiners 

Association, Karen Ellenberger and Hal White, USEPA Office of Underground Storage 

Tanks; Carol Weisner and Joe Abraham, USEPA San Francisco; Maria Tome and John 

Tantlinger, Department of Business, Economic Development, and Tourism, State of 

Hawaii; Andy Goodrich and Daniel Inouye, Washoe County Government, Nevada; 

Tancred Lidderdale, Elizabeth Scott, and Chuck Shirkey, U.S. Dept. of Energy, Energy 

Information Administration; Jeff Kuhn, Montana Department of Environmental Quality, 

Brian Oakland and Syed Nayyer, State of South Dakota; Mandy Easter, State Law 

Library of Iowa; Ross J Andersen, New York State Department of Agriculture and 

Markets; Charlotte Neuner, Missouri Legislative Research; Fred McGarry, New 

Hampshire Dept. of Environmental Services; Mark Toso, Minnesota Pollution Control 

Agency, Jim Glass and Clark Cooney, Oregon Department of Environmental Quality, 

and Fran Rauschenberg USEPA/SEE, Athens, Georgia. 
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