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The API seal of certification on the engine oil product’s container tells you what you need to know about the lubricant’s performance and compatibility with your vehicle. But have you ever wondered what the abbreviation stands for? Learn more about API and what it represents in automotive oil products like engine oil.

What Does API Stand For In Oil Products?

It’s an abbreviation for the American Petroleum Institute (API). The API is the largest American trade association representing the US natural gas and oil industry.

The API produces documents that cover the technical standards and requirements for a wide range of automotive oil-related products and processes. It sets the bar for oil products like diesel engines that ignite fuel using compression, precision thread gauges, and engine oil.

A lot of newer vehicles require specific oil due to being direct injection. Some diesels are also very specific about the oil due to exhaust after treatment.

Anthony Harlin, ASE Certified Master Automobile Technician

Furthermore, the API informs consumers about current standards by annually disseminating physical and digital copies of its technical documents.

API Classification For Engine Oil

The API classifies the service rating of engine oils for passenger and commercial vehicles, ensuring that the oil products deliver the same protection for the engine. Every few years or so, the organization releases a new system that reflects changes and improvements in engine performance and lubrication technology.

SN System

The SN system debuted in 2010. It replaced the older SM system, which dates back to 2004.

S indicates that the category applies to gasoline engines. (For diesel engines, the equivalent designation starts with a C.)

Meanwhile, N indicates that the category applies to vehicles with engines from 2020 or earlier. For comparison, the preceding SM system covers engines built on or before 2010.

The SN system improves on the older system in several ways. SN-compliant engine oils deliver superior protection to cylinder pistons in the high temperatures generated by a running engine. These lubricants also reduce oil sludge and use detergents that don’t degrade oil seals.

Additionally, SN-compliant engine oils reduce the damage and wear dealt to emission and turbocharging systems. They are also compatible with biofuels based on ethanol.

The API evaluates oil products according to the standards set by the appropriate system. If an engine oil passes all tests, the organization approves it for use and distribution.

You can rest assured that an API-approved, SN-compliant engine oil delivers efficient performance at an affordable price. It complies with federal and state legislation, minimizes its environmental footprint, and won’t put you or other people at risk.

SP System

The latest API oil category is the SP system. First presented in May 2020, the new standard requires engine oil products to prevent low-speed pre-ignition (LSPI) and protect engine timing chains from premature wearing.

Compared to products that only meet the older SN system’s standards, SP-compliant engine oils are better at stopping carbon deposits from forming on cylinder pistons and turbochargers at high temperatures. They also have improved control over engine sludge and varnish.

Similar to the SN system, S shows that the product meets the requirement for use in a gasoline engine. Meanwhile, P refers to engines that began production from 2021 onward.

Since far more vehicles on the road date back to 2010-2020, the SN system remains the more relevant category for the time being.

API Oil Certification Meaning

The API sets the performance and quality benchmarks for engine oil. It issues the API Service Symbol Donut to any product that meets the SN system’s stringent standards. You can find this symbol on the product’s label.

The API Service Symbol Donut shows the technical standards that the engine oil meets. In addition to the API rating, it also shows the Society of Automotive Engines (SAE) rating.

SAE Rating

The SAE rating shows the viscosity of the engine oil. You can find it in the prominent center of the API Service Symbol Donut.

The rating has two parts divided by a hyphen. The suffix or first part indicates the ability of the product to operate in cold temperatures. It derives the number from a numerical system for rating oil products. The rating grades are 0, 5, 10, 15, to 25.

Meanwhile, the W stands for winter. If you expect to drive in cold weather, choose an engine oil with a lower SAE rating suffix.

The second half of the SAE rating is a two-digit number. It indicates the oil weight. Also called motor oil viscosity, oil weight is the ability of the engine oil to keep flowing at low temperatures. It also affects how well the oil maintains its lubricating properties at high temperatures.

Many engine oils have an SAE rating of 5W-30. These products are thin enough to continue flowing during winter. They can also keep the engine cool and lubricated in hot temperatures.

If you’re unsure about the manufacturer’s recommended SAE rating for engine oils to use in your vehicle, consult your owner’s manual. It will specify the viscosity grade required for the engine.

API Rating

The API Service Symbol Donut’s outer ring contains the API rating. Here you can find the automotive product’s type, the vehicle’s model year, and the vehicle’s identifier.

Why Does Engine Oil Need API Compliance?

When you buy engine oil, always get a product with an API Service Symbol Donut. An API-certified engine oil offers several advantages.

First, API certification assures consumers that the engine oil product follows a widely recognized quality standard. If the product features an API rating, it can meet the performance requirements expected of motor oil within an operating range.

Second, the API provides a quick way to give you critical information about the engine oil. While it might seem arcane, you can quickly determine the gist of the rating with experience.

Finally, the API rating is recognized throughout the US. Many drivers and practically every mechanic and automotive parts supplier know about it. They’ll immediately understand when you tell them you need engine oil with an API rating of 5W-30.

How Much Does Replacement Engine Oil Cost?

When your vehicle runs low on engine oil, replenish it as soon as possible. A bottle or can of API-certified engine oil can cost anywhere between $10 and $1,950. Its price can vary because of factors like the type and quantity of the oil being sold.

About The Authors
Anthony Harlin, ASE Certified Master Automobile Technician
Reviewed By Anthony Harlin, ASE Certified Master Automobile Technician

Technical Reviewer at

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

CarParts Research Team
Written By Research Team

Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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