Is 87-Octane Gas Always E10?

Why most 87 gas is E10

Ethanol has a high octane value, so blending it into gasoline raises the octane rating of the finished fuel. US refiners commonly produce a lower-octane base gasoline, often called blendstock, that is meant to be mixed with about 10 percent ethanol at the distribution terminal. The ethanol brings the blend up to the 87 rating sold as regular. Ethanol also helps fuel suppliers meet federal renewable fuel requirements and clean-air rules in many areas, which is why E10 became the default across most of the country.

The same approach usually applies to midgrade and premium as well. In most markets, 89 and 91 or 93 octane fuel is also E10. Ethanol content is not what separates regular from premium; the octane rating is.

Octane rating vs. ethanol blend

The two labels answer different questions about the fuel.

Term | What it describes | How it appears at the pump; Octane rating | The fuel's resistance to knock, or premature ignition, in the engine. US pumps show the Anti-Knock Index, the average of the Research and Motor octane numbers, written as (R+M)/2. | A large number such as 85, 87, 89, 91 or 93; Ethanol blend | The share of ethanol in the fuel by volume. E10 means up to 10 percent ethanol; E0 means none; E15 means up to 15 percent; E85 covers high-ethanol blends for flex-fuel vehicles. | A separate sticker or label, where required or provided

Because ethanol raises octane, the two are connected in how fuel is made. But a fuel can reach 87 with or without ethanol depending on the base gasoline used, so knowing the octane tells you nothing certain about the ethanol content.

When 87-octane gas is not E10

Ethanol-free gasoline (E0): Some stations sell gasoline with no ethanol, often marketed as non-ethanol, pure gas or recreational fuel. It is commonly offered at a higher octane, but some locations sell it at 87. E15 blends: Fuel with up to 15 percent ethanol is sold in many areas, often marketed as Unleaded 88 because the extra ethanol raises octane slightly. It is a different product from E10 regular. E0 at marinas and specialty outlets: Fuel sold for boats and small engines is often ethanol-free, though octane varies. Regional differences: Ethanol availability, blending practices and labeling rules vary by state and market, so what is standard in one region may not apply in another. High-altitude markets: In some mountain areas, regular is sold as 85 octane rather than 87. That fuel is typically still E10, but the octane differs.

How to tell what is in the pump

Fuel labeling is your best guide. The octane rating must be posted on the pump. Ethanol disclosure depends on the fuel and the location: many pumps carry a sticker stating that the fuel may contain up to 10 percent ethanol, but whether that sticker is required depends on state rules. Pumps dispensing E15 carry a distinct caution label explaining which vehicles it is approved for. Ethanol-free fuel is usually advertised clearly, since stations market it as a specific product.

If a pump shows only an octane number and no ethanol information, it is reasonable to assume regular gasoline in most of the US is E10, but you cannot be certain without a label or asking the station.

Does it matter for your vehicle?

For most modern cars and light trucks, E10 is the normal fuel the vehicle was designed and approved for, and there is no need to seek out ethanol-free gas. The fuel specification that matters most is the one in your owner's manual or on the fuel-filler door, which lists the minimum octane rating and the maximum ethanol content the manufacturer approves.

Fuel system compatibility becomes more important in a few situations:

E15: The EPA has approved E15 for passenger vehicles from model year 2001 and newer. It is not approved for motorcycles, boats, small engines such as lawn and garden equipment, or older vehicles. Check your manual before using it, since manufacturer approval can differ from the EPA's general allowance. Older and classic vehicles: Some older fuel systems use materials that may not tolerate ethanol well over time. Owners often prefer ethanol-free fuel for these vehicles, though the right choice depends on the specific vehicle and any upgrades it has received. Small engines and boats: Equipment that sits unused for long periods can be more sensitive to ethanol because ethanol attracts moisture. Many owners use ethanol-free fuel or a fuel stabilizer for storage. Flex-fuel vehicles: These are designed to run on blends up to E85, as well as regular E10 gasoline. Only use E85 if your vehicle is identified as flex-fuel.

As for octane, use at least the rating your manufacturer specifies. If the manual calls for 87, a higher-octane fuel generally offers no benefit. If it requires premium, using 87 may reduce performance or cause the engine to adjust its timing to prevent knock. If premium is listed as recommended rather than required, 87 is usually acceptable, with a possible small trade-off in performance.

The bottom line

Most 87-octane gas in the US is E10, but not always. Octane rating measures knock resistance, while the ethanol blend measures how much ethanol is in the fuel, and the two vary independently. Check the pump labels for ethanol content, follow the fuel requirements in your owner's manual, and only seek out ethanol-free fuel or avoid E15 if your vehicle or equipment calls for it.