Summertime Low-RVP Gasoline: Has a Great Idea Run Its Course?

November 12, 2026

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by Paul Machiele (Stillwater Associates) Low-RVP summer gasoline was a great idea when Congress and the U.S. Environmental Protection Agency (EPA) adopted it more than 30 years ago. Gasoline with a Reid vapor pressure (RVP) below 9.0 pounds per square inch (psi) delivered large, cheap cuts in ozone-forming emissions. The evidence now points to a different balance: today’s vehicles have erased most of that benefit, while the cost to consumers and the strain on gasoline supply remain. The summer of 2026, when EPA and most states set these programs aside, gives policymakers new information to weigh. This article walks through what has changed, what 2026 showed, and the choices ahead.

The Backdrop

In the late 1980s, EPA had a great idea for fighting summertime ozone: cut the volatile organic compound (VOC) emissions that evaporate from gasoline by reducing summer RVP back down to 9.0 psi, the level at which manufacturers certified their vehicles and the level ASTM International had identified as necessary for vehicle operation and driveability.[1] It was such a good idea that Congress wrote it into Section 211(h) of the Clean Air Act (CAA) in 1990.

But if some RVP control was good, then more must be better. Vehicle testing at the time showed that lower RVP cut exhaust emissions too, because it helped vehicles hold a stoichiometric air/fuel ratio while they purged the evaporative canister. Add the reductions from nonroad equipment, gas cans, and the fuel distribution system, and gasoline below 9.0 psi was a no-brainer.

So, in Section 211(k) of the CAA, Congress also mandated reformulated gasoline (RFG) in the nation’s worst ozone nonattainment areas and required it to cut VOC and air toxics emissions by 25% from 1990 baseline gasoline. Refiners’ primary lever for hitting those targets was lowering RVP further, to about 7 psi. A number of states jumped on the bandwagon to meet their ozone State Implementation Plan obligations, some by opting into RFG and more by adopting their own “boutique” standards between 7.0 and 7.8 psi.

The price was right. Then as now, pulling butane out of summer gasoline cost roughly 2 cents per gallon and reduced gasoline supply by about 2% for each psi of RVP reduction (EPA’s most recent estimates are in the same range). In return, it delivered large, immediate VOC reductions.

Shifting Impacts Over Time

Fast forward to today, and much of that picture has changed.

Start with the vehicles. Tier 3 emission standards took effect in 2017 and phased in through 2025. They have driven technology to the point that, on Tier 3 and newer light-duty vehicles, evaporative emissions tied to the gasoline itself are essentially gone. What the evaporative emissions test still picks up comes mostly from the vehicle’s plastics, polymers, and rubbers.

Electronic controls have also eliminated the exhaust benefit that low RVP used to provide. In fact, EPA’s testing of Tier 2 (2008 model year) vehicles showed that RVP below 9.0 psi increased exhaust VOC emissions. Nearly the entire in-use fleet is now Tier 2 or newer.

Consumer nonroad equipment is increasingly going electric, which eliminates its in-use emissions along with any effect of low-RVP gasoline. Existing emission models do not appear to have caught up with that shift. On top of that, as nitrogen oxides (NOx) emissions have come down, many areas have become NOx-limited. In those areas, NOx reductions matter far more for summertime ozone than VOC reductions do, and evaporative VOCs in particular tend to be less reactive.

Meanwhile, cost and supply have become the primary concern. Butane removal still costs money and volume.

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This year, to increase gasoline supply and lower prices, the Trump administration issued a nationwide emergency fuel waiver on March 25, 2026. Under it, EPA would not enforce RVP limits below 9.0 psi, or below 10.0 psi for gasoline blended with 9% to 15% ethanol. EPA renewed the waiver through the summer and, in late August, brought the switch to winter gasoline forward to September 1, two weeks early. I covered what it did, and what it did not do, at the time.

State Actions

States have been weighing the same tradeoff between air quality benefit and cost to their consumers. According to Herman Associates, New York, New Jersey, California, and Connecticut kept their own standards in place for the summer of 2026 rather than matching the federal waiver.

But 2026 was only the latest development. Since 2012, nine states (Alabama, Illinois, Georgia, Ohio, Maine, Pennsylvania, Kansas, Missouri, and Kentucky) have steadily eliminated their low-RVP programs.

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Dropping RFG adds about 0.5 tons of VOC per summer day in 2026 to an area inventory of roughly 74 tons, an increase of less than 1% (91 Federal Register 10008, March 2, 2026). Roughly two-thirds of that small increase, 0.3 tons, comes from nonroad equipment, and MOVES doesn’t yet reflect how fast that equipment is going electric.

Several states have kept their programs on the books out of concern that eliminating them could give up air quality benefits. Those programs include California RFG, Arizona’s Cleaner Burning Gasoline (CBG) in Phoenix, 7.0 psi standards in Detroit and El Paso, and a 7.8 psi standard in East Texas.

The CAA also still mandates RFG in the country’s most severely ozone-polluted areas. When EPA streamlined the RFG standards in 2020, it kept the RVP cap at the existing 7.4 psi.

2026: A Natural Experiment

In March, I wrote that this summer would function as a natural experiment. Reading the results takes some care, because ozone is hard to pin on any one program. Summertime ozone levels depend on temperature, sunlight, wind, and weather patterns such as temperature inversions, all of which change from day to day and year to year, and each area experiences emissions from a host of different sources. For these reasons, from one year to the next there is roughly a 50% chance that the number of ozone exceedances will go up or down. Picking out the effect of a single emission control program in a single year is close to impossible, and it is harder still for a program that current emission models show has a small effect on VOC emissions.

With that caveat, a look at the withdrawal of most low-RVP programs this summer may offer some insight. I pulled up data for nine RFG areas at 7.4 psi and three state boutique fuel areas at 7.0 psi that relaxed their RVP standards for 2026 and for which EPA also posted 2026 ozone data.[2] I counted the days from May through September when the daily maximum 8-hour ozone level in each area exceeded 0.070 parts per million, the level of the current federal standard. Only three of those areas had more such days in 2026 than in 2025. Only one (Denver) had more than its average for the previous three years, a comparison that smooths out influences other than RVP. Denver, which appears in both counts, was clearly an outlier in 2026, with four times as many exceedance days as the year before. Colorado’s Regional Air Quality Council attributed the season mainly to heat and dry, sunny weather, with wildfire smoke adding to ozone on some days.

Even with no change in emissions, the other factors that influence ozone would have led roughly half of these areas to see more ozone in 2026 and half to see less. That ozone levels mostly declined in 2026 (despite the impact of the Canadian wildfires) is certainly happenstance. But it does highlight the key point. If low-RVP gasoline were doing meaningful work, taking it away should have pushed these areas toward more ozone exceedances, not fewer. Whatever effect it had was too small to see through the normal year-to-year variation.

As it turned out, since some states in the East Coast RFG area relaxed their requirement and others did not, another natural experiment occurred. I performed a similar analysis looking at four cities in this area for which EPA posted 2026 ozone data. The two areas that did relax their RVP standard (Baltimore, MD and Washington, D.C.) experienced fewer ozone exceedances in 2026 than the prior three-year average. For the two areas that did not relax their RVP standard (New York, NY and Hartford, CT), New York City also experienced fewer ozone exceedances in 2026 but Hartford experienced a slightly higher number of ozone exceedances. Again, the areas that relaxed RVP fared no worse than the areas that kept it, which supports the same conclusion: the impact of low-RVP programs is in the noise.

The pattern matches earlier natural experiments, when states eliminated their low-RVP programs. Across the eight state actions with at least three years of post-change data (two of them for Atlanta, and one covering both Kansas and Missouri),[3] 8-hour ozone exceedances rose in only two when I compared the three years starting with the effective date to the three years before. In both cases, a single outlier year drove the increase.

One year of ozone data will not settle the question in everyone’s minds, and more sophisticated analyses of the data can and should be done. But I expect they will confirm what MOVES already indicates: low-RVP programs do not have a first-order effect on ozone levels.

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Absent further action, the low-RVP requirements stay on the books for next summer and beyond, resting on data and understanding from more than three decades ago, without any current technical basis, and despite their high cost and impact on gasoline supply. Absent new vehicle testing, inventory modeling, and air quality modeling of the real-world ozone impact of low-RVP programs, EPA, the states, and Congress each have a choice to make, and the evidence above bears on all three.

EPA could raise the RVP limit for RFG from 7.4 psi to 9.0 psi, or perhaps to 10.0 psi.
States with their own programs, including California with its RFG and Arizona with CBG, could relax or eliminate their RVP requirements, as nine states have done since 2012. Each would likely need to show EPA, as Kentucky did, that the change would not interfere with meeting the ozone standard, a showing that should be based on updated data and science able to quantify the impacts today.
Congress has the cleanest and most effective option: make permanent what the 2026 waiver allowed. That would mean eliminating the federal RFG program, so that EPA regulates all gasoline the way it regulates conventional gasoline today. It would also mean revising Section 211(h) to set 10.0 psi as the RVP limit for all gasoline nationwide, with 9.0 psi as the base level for gasoline blendstocks headed for ethanol blending.

This past summer’s natural experiment is consistent with EPA’s MOVES modeling – these changes would have little or no effect on ozone. They would, however, make permanent the lower gasoline costs (roughly $3 billion a year nationwide, including about $400 million a year in California alone), the added supply, and the protection from supply disruptions that come with eliminating low-RVP programs.

Anyone weighing these choices needs to examine how much emission benefit the program still delivers with today’s fleet, what the program costs in supply and price, and what a noninterference demonstration would have to show. READ MORE

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EPA’s summer fuel waiver goes further than it looks, but does it mean an E15 boom? (Stillwater Associates)

Excerpt from Stillwater Associates: Rather than simply allowing E15 to be sold alongside E10 during the summer volatility control period, this action effectively eliminates the country’s patchwork of boutique summer fuel formulations, creating a single national gasoline pool at 9-15% ethanol content under a common 10 psi Reid Vapor Pressure (RVP) standard.

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In a recent Stillwater article, I traced the decades-long regulatory and commercial struggle to establish E15 as a viable mainstream fuel. That analysis concluded that the RVP waiver (the very issue that EPA’s March 25 action addresses) was never the primary obstacle to broader E15 adoption. The more durable constraint is retail infrastructure – stations built and certified to E10 standards, insurers being unwilling to provide coverage without compatibility documentation, and upgrade costs that can exceed $1 million per location.

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The Air Quality Picture in a Modern Fleet

The air quality implications of this waiver are directionally toward higher volatile organic compound (VOC) emissions – but materially smaller than they would have been when the low-RVP standards were established in the late 1980s and early 1990s. The original standards were designed for a vehicle fleet with carburetors and early injectors, mechanical diaphragm fuel pumps susceptible to vapor lock, and first-generation evaporative emission control systems that could not contain vapor above 9 psi. Today’s fleet is fundamentally different. Modern vehicles use electric in-tank fuel pumps immersed in liquid gasoline, greatly reducing vapor lock risk. Evaporative emissions from properly operating modern vehicles are effectively zero – activated carbon canisters and sealed fuel systems handle vapor effectively, and refueling emissions are reduced by onboard vapor recovery systems required since the 1990s.

The reason the air quality calculus has shifted comes down to how modern engines actually use fuel. Volatile components like butane and pentane (the same compounds that raise RVP) improve cold-start and heavy-acceleration combustion efficiency, which is now the dominant source of vehicle exhaust emissions. Remove them, and exhaust emissions go up. Research on modern Tier 2 and newer vehicles bears this out; lower RVP gasoline is associated with increases in VOC emissions as well as NOx and other pollutants. The net effect depends on local conditions, but in many areas, lowering summer RVP below 9 psi may provide little or no air quality benefit while reducing gasoline supply and putting upward pressure on prices. Summer volatility control was a cost-effective tool when it was introduced in the early 1990s, but applied to today’s fleet, the tradeoff looks considerably less favorable.

The main air quality concern with the 2026 action is localized: extreme heat markets like Phoenix, where canister breakthrough is a real risk at 10 psi. The broader story is that this summer will function as a natural experiment – the first large-scale real-world test of how observable the RVP/ozone relationship is across the modern vehicle fleet operating at higher summer RVP levels. The data should be valuable.

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What it may do is something more modest but still useful: a common national blendstock makes E15 incrementally easier and cheaper to supply, potentially improving the economics that underpin infrastructure investment decisions. That along with the low price of ethanol compared to gasoline may help stimulate the long awaited nudge to meaningfully accelerate the all-important retail build-out of E15. READ MORE