When choosing engine oil, you’ll often see ratings like API SN, SP, or SQ on the bottle.
These letters are not just marketing terms — they represent engine oil performance standards set by the API (American Petroleum Institute).

Understanding these standards helps you choose the right oil for better engine protection, fuel efficiency, and longevity.

What Is API Engine Oil Classification?

API classifications indicate the performance level of engine oil for gasoline engines.

The letter “S” stands for Spark ignition (petrol engines)

The second letter (N, P, Q…) shows the generation and performance level

The later the letter, the newer and more advanced the oil

Each new API standard is designed to meet the needs of modern engines, including:

Turbocharged engines

Direct injection (GDI)

Start-stop systems

Better fuel economy and lower emissions

1. API SN — Reliable Protection for Older Engines

API SN was introduced to improve engine cleanliness and oxidation resistance compared to older standards.

Key Features:

Good engine wear protection

Improved sludge and deposit control

Compatible with older gasoline engines

Suitable for:

Vehicles manufactured before ~2018

Naturally aspirated engines

Older engine designs without high turbo stress