You might have noticed that many gas stations West of the Rockies top out at 91 octane. This isn’t just a regional quirk; it’s a result of a complex interplay between environmental regulations, infrastructure, vehicle technology, and regional driving conditions. While higher octane fuel can improve engine performance and keep your DAM from dropping below 1.00, stringent emissions standards, particularly in California, have led to fuel formulations that prioritize cleaner burning over raw power. This has resulted in a lower top-tier fuel grade in many areas, even if it might not be ideal for some performance-oriented, turbocharged or high compression engine-powered cars & trucks.
I’m going to step back & give a quick refresher on fuel octane, just to make sure I’ve been thorough. Octane as a raw definition is an isomeric saturated hydrocarbon found in petroleum and used as a fuel and solvent. Arranged as a single, two electron, covalent bond: C8H18 
Alas, this will muddy the water farther, energy producers don’t use pure octane as a means to formulate or modify gasoline. They use other chemicals, elements & hydrocarbons. Things like Lead, MTBE, ethyl-benzene, toluene, xylene and ethanol. Some of these are oxygenates (bonds carrying an extra oxygen atom available to be cracked during combustion leading to a cleaner & leaner burn) are highly toxic, heavy or hard to get rid of. Some refineries may not want to fuss with some of these gnarly chemicals if they’re dealing with California but we’ll get back to oxygenates and California later.
Octane ratings, as described by the US Energy Information Administration are measures of fuel stability. These ratings are based on the heat & pressure at which a fuel will spontaneously combust (auto-ignite) in a testing engine. The octane number is actually the simple average of two different octane rating methods—motor octane rating (MON) and research octane rating(RON)—that differ primarily in the specifics of the operating conditions. The higher an octane number, the more stable the fuel. Thank you US EIA! So we’re quantifying a fuel's ability to resist two major modes: pre ignition, an abnormal combustion event that can lead to colliding flame fronts in the combustion chamber leading to destructive cylinder pressure spikes or abnormal combustion known as detonation which is just that, a singular explosion event, also plenty destructive. Both of these abnormal combustion conditions can lead to audible “pinging” or spark knock, or just plain knock. Higher octane fuels are more resistant to these conditions, allowing engines to operate at high boost and/or higher compression ratios with more advanced ignition timing. This translates to increased power and efficiency with fewer broken engine parts due to larger margin of safety.
Post WW2 Los Angeles was a bustling hub of industry: aerospace technology, film studios, electronics manufacturers, oil exploration and military bases, to name a few. A booming high tech economy in beautiful area with mountains & beaches with only two seasons per year experienced a population boom followed by a building boom. Los Angeles also led the country in pioneering zoning requirements separating established industrial areas, urban areas and suburban areas. This new “gold rush” of folks living in the suburbs and working in the industrial or urban areas coupled with post war prosperity of regular folks owning automobiles, sometimes multiple automobiles, gave way to commuting traffic. Southern California was now occupied by fleets of big swoopy, chrome-laden chubby fendered cars with squishy supple suspension powered by big displacement iron. A large fleet of big inch cars drove an estimated combined total of 8 billion miles in the LA area in the early 1940s. A strange phenomenon was about to occur. The first recognized episodes of smog occurred in the summer of 1943. Visibility was reduced to mere blocks; residents suffered from burning eyes, lungs, and nausea. Initially, the "gas attack" was blamed on a nearby butadiene plant. However, even after the plant's closure, the smog stuck around.
In 1948, Arie J. Haagen-Smit, a chemistry professor at the California Institute of Technology, began investigating the cause of the smog. He discovered that the culprit was not industrial emissions but rather automobile exhaust. Haagen-Smit's groundbreaking research revealed that sunlight reacted with pollutants from car exhaust, creating photochemical smog. This smog contained harmful ozone, nitrogen oxides, and other toxic chemicals.
Recognizing the severity of the air pollution crisis, California took action. In 1947, the Los Angeles County Air Pollution Control District was formed, the first of its kind in the nation. This district focused on regulating obvious pollution sources like power plants and refineries. However, as the role of automobiles became clearer, stricter regulations were coming.
The discovery of smog in Los Angeles and the subsequent establishment of CARB marked a significant turning point in air pollution control. California's pioneering efforts in air quality regulation have served as a model for other states and countries, demonstrating the importance of science-based policies and regulatory measures to protect public health and the environment.
You may be asking yourself: why is this article so California centric? Population & logistics play a major role, coupled with California’s self proclaimed need to be our leading emissions innovator & repentant revolutionary. When the EPA set forth with gasoline reformulation and stricter limits on the use of lead in 1990, CARB said “hold my beer!” CaRFG1 or California gasoline reformulation 1 effectively banned leaded gasoline for use in road going motor vehicles in addition to limiting fuel volatility. Voila! 93 octane and above have disappeared from the Western US. 92 octane is the new standard in high octane fuel. In 1996, new California standards CaRFG2 mandated even tighter limits on “aromatic additives” or likely octane boosters, carcinogens were cut by 1/3 and now fuel is required to be oxygenated, year round. CaRFG2 mandated the use of even more MTBE (Methyl tertiary-butyl ether) an octane booster and oxygenate, also later famous for requiring gas station & land owners to dig up fuel tanks to remediate groundwater leeching concerns. Who remembers that purple racing fuel that made injectors swell? That had a decent bit of MTBE in it.
Union Oil California was ahead of the curve, seeing the writing on the wall, were busy in r&d in the early 1990s. They earned patents on the first five of the new 92 octane gasoline formulations. Refineries & other oil companies not wanting to be gouged by licensing fees chose to litigate with Unocal. These legal battles went on for six years, ending with a whimper. In 2001, Kinder-Morgan, the owner of most of the West’s pipelines, surveyed their retail customers. Their retail customers were asking for a cheaper & more readily available alternative to Unocal’s 92 octane. Other oil companies and refineries had easy access to raw stocks to produce 91 octane, thus Kinder-Morgan’s California dealings sealed your tuner’s fate. As California goes, so goes the Western United States. It’s much cheaper to pipeline fuel long distances from refineries and then truck it out using local hubs. While in places like Colorado, Montana, New Mexico, Utah & Wyoming, you may hear folks suggest you don’t need octane because you have altitude. Know that in the case of a high performance engine, too many oxygen molecules in the atmosphere won’t hold back your horsepower but lack of knock resistance will.
So you’ve made it this far. We can help you & your 91 octane powered beast. Not all 91 octane formulations are identical, there are small regional changes made to the California friendly swill that they pipe out west. As a Cobb Tuning dealer & Protuner supporting the Subaru, GTR & Porsche platforms, we offer custom calibration, maintenance and installation. We also stock a multitude of high end fluids, including two different octane enhancements- one simple pour in and forget it: Hi-Test by Maxima and the other is Race Fuel Concentrate which requires calculated mixing, capable of mixing pump gas up to 105 octane.
