Bitumen is the heaviest and thickest form of petroleum. While the question of "heaviest oil" can refer to different contexts (e.g., crude oil, motor oil, gear oil), bitumen consistently holds the title for the heaviest form of petroleum.
Understanding Different Types of "Heavy" Oil
The term "heavy" in the context of oil can be ambiguous. It can refer to:
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Crude Oil Viscosity: Heavy crude oil, or extra heavy crude oil, is highly viscous and doesn't flow easily from wells. Wikipedia's entry on Heavy Crude Oil details this characteristic.
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Motor Oil Viscosity: Motor oil viscosity is measured using the SAE (Society of Automotive Engineers) system. Higher numbers indicate thicker oil. For example, 10W-60 is thicker (and considered "heavier" in this context) than 5W-30. Discussions on forums like CorvetteForum and Honda-Tech show varied recommendations for motor oil weight based on engine type and manufacturer specifications. Note that using an oil heavier than recommended can negatively impact engine performance and longevity.
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Gear Oil Viscosity: Similar to motor oil, gear oil viscosity is also determined using an SAE system. Higher numbers signify thicker, heavier oil. Examples of heavier gear oils and their uses can be found in discussions such as this one on SlingshotForums.
Specific Examples and Considerations:
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Bitumen: Used for road surfacing, roofing, and other applications. It's significantly thicker than any motor or gear oil.
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Heavy Crude Oil: Requires specialized extraction and refining processes due to its high viscosity.
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Motor Oils: The "heaviest" motor oil suitable for a specific engine is dictated by the manufacturer's recommendations and not a universally applicable number. Using oil outside these recommendations may harm the engine.
