What is Oil?
Oil may seem like a single substance, but in reality, there are many different kinds of oil—each with its own physical and chemical characteristics. These differences affect how oil behaves when spilled and how it impacts the environment. Three key properties used to classify and understand oil are its viscosity, volatility, and toxicity.
- Viscosity – This refers to an oil’s resistance to flow. Thick oils, like heavy crude or bunker fuel, have high viscosity and flow slowly. Light oils, such as gasoline or diesel, have low viscosity and flow more easily. Viscosity influences how far oil spreads after a spill and how difficult it is to clean up.
- Volatility – This refers to how quickly an oil evaporates into the air. Highly volatile oils, like gasoline, can evaporate rapidly, sometimes posing inhalation or fire hazards. Less volatile oils tend to persist longer in the environment, making cleanup more difficult.
- Toxicity – This describes how poisonous an oil is to humans, animals, or plants. Some oils contain more harmful chemical compounds than others. Toxicity affects the level of risk to marine life, birds, soil, and water quality after a spill.
When oil is spilled, these three properties determine how it behaves in the environment—how far it travels, what kind of damage it causes, and what cleanup strategies are most effective. For example, a light, volatile oil may evaporate quickly but pose immediate health risks, while a thick, less volatile oil may linger and cause long-term environmental damage.
The Four Types of Oil
When spilled, the various types of oil can affect the environment differently. They also differ in how hard they are to clean up. Spill responders group oil into four basic types, which you can see here, along with a general summary of how each type can affect shorelines.
Type 1: Very Light Oils (Jet Fuels, Gasoline)
- highly volatile (should evaporate within 1-2 days)
- high concentrations of toxic (soluble) compounds
- localized, severe impacts to water column and intertidal resources
- no cleanup possible
Type 2: Light Oils (Diesel, No. 2 Fuel Oil, Light Crudes)
- moderately volatile and will leave residue (up to one-third of spill amount) after a few days
- moderate concentrations of toxic (soluble) compounds
- will "oil" intertidal resources with long-term contamination potential
- cleanup can be very effective
Type 3: Medium Oils (Most Crude Oils)
- about 1/3 will evaporate within 24 hours
- oil contamination of intertidal areas can be severe and long-term
- oil impacts to waterfowl and fur-bearing mammals can be severe
- cleanup most effective if conducted quickly
Type 4: Heavy Oils (Heavy Crude Oils, No. 6 Fuel Oil, Bunker C)
- little or no evaporation or dissolution
- heavy contamination of intertidal areas likely
- severe impacts to waterfowl and fur-bearing mammals (coating and ingestion)
- long-term contamination of sediments possible
- weathers very slowly
- shoreline cleanup difficult under all conditions
Knowledge Check Choose the best answer for the question.
2-2. How much spilled medium type crude oil should evaporate in 24 hours?
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