The specific gravity of light oil isn't a fixed number but rather a range, typically described using API gravity, with values exceeding 38 degrees API.
Understanding Specific Gravity and API Gravity
Specific gravity is a measure of a substance's density compared to the density of water. However, in the oil industry, API (American Petroleum Institute) gravity is more commonly used. It’s an inverse scale, meaning higher API gravity corresponds to lower specific gravity (and thus, lighter oil) and vice-versa.
API Gravity and Crude Oil Classifications
The reference provides a useful way to categorize crude oil types:
| Crude Oil Type | API Gravity (Degrees) |
|---|---|
| Light Crude | > 38 |
| Intermediate Crude | 22 - 38 |
| Heavy Crude | ≤ 22 |
Light Crude Oil Specific Gravity
Because API gravity and specific gravity have an inverse relationship, and light crude has an API gravity of over 38 degrees, it has the lowest specific gravity among crude oils. We can say the specific gravity of light oil is below approximately 0.83.
- Calculation Note: API gravity and specific gravity (SG) can be approximately converted using the formula: API = (141.5 / SG) - 131.5. Conversely, Specific Gravity (SG) can be calculated as: SG = 141.5 / (API + 131.5).
- Using the API threshold of 38 degrees for light oil, we can roughly calculate a maximum specific gravity of light oil using the calculation: SG = 141.5/(38+131.5) = 0.83.
- In practice, Light oils can have a specific gravity lower than this, depending on their individual API degrees
Key Takeaway
- Light crude oil is characterized by a high API gravity (above 38 degrees) and a correspondingly lower specific gravity (below approximately 0.83).
- Instead of specific gravity, the industry uses API gravity, making it easier to differentiate between crude oil types.
