The Clean Air Act, as amended, provides the basic statutory framework for the role of the federal government and the states in managing air quality in the United States. Among other things, the Act authorizes EPA to set and enforce standards, referred to as National Ambient Air Quality Standards (NAAQS), for pollutants. EPA has subsequently set standards for six pollutants—ozone, particulate matter, carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead. While carbon monoxide is directly emitted when various fuels are burned, ground-level ozone is formed when VOCs and NOx mix in the presence of heat and sunlight. As a result, emissions of VOCs and NOx are considered by EPA and the states in their efforts to reduce concentrations of ground-level ozone. Because heat and sunlight act as catalysts in the formation of ground-level ozone, high ozone levels are most prevalent in spring and summer. EPA sets and enforces the NAAQS to, among other things, reduce the negative health effects of air pollution. Each of the six pollutants covered by the NAAQS is known to cause a variety of adverse health and other consequences. For example, at certain concentrations ground-level ozone and carbon monoxide can, among other things, cause lung damage, eye irritation, asthma attacks, chest pain, nausea, headaches, and premature death. To enforce the standards, EPA evaluates monitoring data on air quality to determine whether local air quality meets federal standards—designating areas as in either attainment (if they meet the federal standards) or nonattainment (if they do not meet the federal standards) with each of the NAAQS. Under the Act, states that contain areas in nonattainment with the NAAQS are required to identify how they will reduce emissions and improve air quality to meet them. For each pollutant, states are required to prepare a state implementation plan (SIP) and have the plan approved by EPA. States have choices in determining how to reduce emissions and meet air quality standards, determining, among other things, how much to reduce emissions from mobile sources such as automobiles compared with other sources of similar emissions such as power plants. Because use of gasoline in automobiles emits several chemicals, including carbon monoxide, nitrogen oxides, and VOCs, and because emissions from automobiles are often an important contributor to local air quality problems, the federal government and the states often focus on reducing automobile emissions. Whatever the planned reductions, states must identify an inventory of air emissions and demonstrate in their SIPs how they will achieve attainment in a specific time frame. States typically demonstrate this through modeling analysis that estimates how the various efforts in their SIPs will reduce emissions and improve air quality. The Act also provides authority to set standards and establish requirements for some programs specifically designed to reduce vehicle emissions. For example, using authority provided under the Act, EPA has required newer cars to meet more stringent emissions standards, and vehicle manufacturers have incorporated emissions-control devices such as catalytic converters and oxygen sensors to meet them. Further, the Act requires cars to have under-the-hood systems and dashboard warning lights that check whether emissions control devices are working properly. In addition, the Act requires that some areas—generally highly populated metropolitan areas—have programs for periodic inspection and maintenance of vehicles. These programs identify high-emitting vehicles, which sometimes have malfunctioning emissions control devices, and require vehicle owners to make repairs before the vehicles can be registered. The Act gives the federal government, through the EPA, primary authority for regulating the environmental impacts of gasoline use. For example, the Act sets minimum national standards for conventional gasoline, as well as requiring that certain gasoline blends formulated to reduce emissions be used in some areas with especially poor air quality. Specifically, for certain areas with long-standing and especially poor air quality, the federal government requires the use of special reformulated gasoline, commonly referred to as RFG. The amendments also require other areas to use special gasoline blends designed to reduce summertime ozone pollution and wintertime carbon monoxide pollution. The Act allows states or regions not required to use RFG to seek EPA approval to require use of other special gasoline blends to aid in improving air quality, provided that they do not violate minimum federal standards. In 2001, EPA studied the proliferation of gasoline blends and reported that several states had chosen special blends other than RFG for one or more of three reasons: (1) the states were not eligible to require RFG because their air quality was not bad enough, (2) the states wanted to avoid the RFG requirement to use an oxygenate and its added cost, (3) fuel suppliers and states believed that the other special blend would be less costly than RFG while meeting their need to reduce emissions. States seeking to use a special gasoline blend must obtain formal approval from EPA, generally the regional office with authority to review their SIPs. Specifically, under the Clean Air Act, section 211(c)(4)(C), EPA may approve applications by states to use special gasoline blends if the states demonstrate that the fuel is needed to reach attainment with federal air quality standards. In guidance issued in August 1997—after several of the special gasoline blends were approved—EPA clarified that they can approve a state gasoline requirement only if “no other measures that would bring about timely attainment exist,” or if other measures are “unreasonable or impracticable.” The guidance requires that states do four things in their application for approval of a new or revised SIP: (1) quantify the estimated emissions reductions required to reach attainment with the federal NAAQS for ozone; (2) identify possible control measures that could be used in place of special gasoline blends and provide emissions reduction estimates for those measures; (3) explain why those measures are “unreasonable or impracticable”; and (4) show that, even with use of all “reasonable and practicable” measures, additional emissions reductions are needed. As is the case with other new or revised SIPs, these applications are open for public comment, and EPA must consider those comments before making a decision. Once approved, states’ special gasoline blends become federally enforceable requirements. Under some circumstances, EPA may temporarily waive special gasoline blend requirements, referred to as granting enforcement discretion, if, for example, the required special gasoline blend is not available due to a supply disruption. Over the past several years, EPA has waived the requirement to use these special gasoline blends on several occasions when it determined that overall supplies might become tight. We found that EPA has granted enforcement discretion on at least 23 occasions, allowing gasoline that did not comply with local requirements to be sold there. The causes of these supply disruptions included the 2003 blackout in the Northeast, the series of hurricanes in Florida and the Gulf Coast in 2004, as well as refinery fires, pipeline breaks, and other infrastructure problems. Although there was one short waiver that applied nationwide following the terrorist attacks of September 11, 2001, several of the other waivers were provided to local areas with particularly stringent gasoline formulations including St. Louis, Chicago/Milwaukee, Atlanta, Las Vegas, and Phoenix when there were supply shortages in these areas. All gasoline is a blend of different components that are predominantly produced in refineries. The simplest refineries primarily separate the components already present in crude oil. More complex refineries also have the ability to chemically change less valuable components of crude oil into more valuable ones. Because of their ability to chemically alter components, complex refineries can increase the amount of gasoline yielded from a given amount of crude oil and reduce the amount of less valuable products. Although most refineries can process many types of crude oil, refineries are generally configured to run most efficiently when refining a specific type of crude oil into a specific group of products. Absent specific regulatory requirements, refiners blend several components derived from crude oil to produce a gasoline that achieves acceptable engine performance at the lowest cost. Two key aspects of gasoline affect engine performance: Reid vapor pressure is a measure of gasoline’s tendency to evaporate and also reflects the ease with which it ignites when the spark plug fires in a cold engine. To maintain engine performance, RVP must vary by season and region. Higher RVP is required in colder climates and seasons to allow an engine to start. Octane number is a measurement of gasoline’s tendency to ignite without a spark, commonly known as “knocking” in a running engine. Some high-performance and other vehicles require gasoline with a higher octane number. To satisfy these requirements and consumer demand, retailers in the United States typically sell three different octane grades of gasoline. Special gasoline blends developed to reduce pollution are generally adjusted in at least one of the following ways: RVP is reduced during the summertime to reduce VOC emissions. Reducing the RVP of gasoline requires reducing the amount of very light compounds, such as butanes and pentanes, blended into the gasoline. Toxics, their precursors, or other chemicals are limited so they are not released into the air when the gasoline is burned. Some of these, such as sulfur, naturally occur in crude oil while others, such as benzene, result from gasoline refining. Oxygenates, chemical compounds containing oxygen to aide in combustion, are added to gasoline to improve environmental performance when the gasoline is burned, including reducing carbon monoxide (CO) emissions. The most commonly used oxygenates are MTBE and ethanol. Several states have banned MTBE as a result of concerns about groundwater pollution and have switched to using ethanol as an oxygenate where required. Gasoline is shipped from U.S. refineries to consumers by some combination of pipelines, water barges, rail, and trucks to retail gasoline stations. Most of the country’s refining capacity is located in the Gulf Coast, West Coast, East Coast, or Midwest with only a small amount in the Rocky Mountain states.