Octane Rating

Gasoline octane rating is a measure of resistance to knock. So what exactly is "knock"? It's that metallic ping sometimes heard during hard acceleration or when a heavy load is being pulled up a steep hill.

Gasoline should burn smoothly in your engine, starting with the flame at the spark plug and progressing across the combustion chamber. However, under certain conditions—like a lower octane—gasoline can detonate prematurely. Today's engines have knock sensors to sense the onset of knock and a computerized engine management system that adjusts the spark timing. This computerized "detuning" of the engine can prevent knock in the first place. It's all well and good, except a detuned engine has less power, resulting in less efficient use of gasoline.

The best way to avoid knock and keep your engine running its best? Use the recommended octane level for your vehicle. Engines recommended to run on premium fuels can benefit the most from high octane gas.

Want to learn more? Go to www.FuelCertification.com.

Learn about other key measures of gasoline.

View Transcript

7 easy ways to keep your car running smoothly
Choose a gas like BP gasoline with Invigorate®
that, with continuous use, can help fight performance-robbing deposits on critical engine parts, helping to maintain engines and restore fuel economy.*
Get regular tune-ups.
Tune-ups can improve your car's performance and gas mileage**.
Drive smart.
Gas mileage usually decreases at speeds over 60 mph, so by observing the speed limit, you can save gas. On long trips, cruise control can also help (when safe to engage).***
Inflate your tires properly.
In addition to improving your gas mileage, properly inflated tires last longer and give you a safer drive.***
Lighten up already.
Extra weight decreases gas mileage. Remove unnecessary items from your trunk, and, if you have a removable roof rack that's never used, take it off.***
Turn off the car.
Idling is a waste of fuel. When it's safe to do so, it's better to turn off the engine and restart a few minutes later.
Give your car regular washes.
A clean vehicle helps protect against body damage caused by heat, bugs, emissions, salt and the effects of time. And to help clean critical engine parts, use BP gasoline with Invigorate.

BP's Policy on MMT

MMT (Methylcyclopentadienyl Manganese Tricarbonyl) is a gasoline additive that enhances octane to reduce knock. In 1978 the U.S. Environmental Protection Agency banned its use in unleaded gasoline, but it's been used in Canada for the last 20 years. To date, there have been no studies on the potential health impacts of the particles of manganese in MMT's combustion emissions, but MMT remains controversial.

The manufacturer of MMT eventually won a court battle with the U.S. EPA that allowed it to sell MMT for use in conventional, unleaded gasoline at a maximum level of 1/32g manganese per gallon of fuel. Despite this legal victory for MMT, BP is not aware of any major U.S. gasoline retailer using MMT in its products.

Additionally, automobile and equipment manufacturers have expressed concerns regarding the negative effects of MMT on mechanical equipment. According to GM, Ford and Chrysler, MMT can damage catalytic converters, on-board diagnostics systems, oxygen sensors, EGR valves and spark plugs, all of which can lead to higher pollution levels. Statements warning car owners of the potential detrimental effects of MMT can be found in many automakers' owner manuals.

As a matter of policy, BP does not use MMT in its U.S. gasoline.