What does the word 'oil' bring to mind? You may think of runny yellow liquid, like vegetable oil in the kitchen cupboard, or hair oil in the bathroom.
There's another important type of oil to think about – crude oil. It resembles treacle; a dark, sticky liquid. Crude oil is one of the three fossil fuels: coal, natural gas, and crude oil.
Ready to fuel your knowledge? Dig into this article!
Let's begin with the definition of fuel.
A fuel is a physical substance that can be consumed to produce energy.
Usually, this consumption refers to combustion (a.k.a. burning). But not always. Ever heard the expression 'food is fuel?' It's true – our body consumes food by breaking down molecules during digestion. When the bonds between molecules are broken down, energy is released. Our bodies use this energy to maintain essential functions and perform physical movement.
Examples of fuels include coal, hydrogen, bioethanol, and wood.
What is the Difference Between Fuel and Oil?
The Importance of Crude Oil as a Fuel
Let's recap the definition of crude oil.
Crude oil (also called petroleum) is a thick, unrefined mixture of hydrocarbon compounds.
The colour of crude oil depends on its chemical composition. For example, crude oil with few metals or sulfur-based compounds is light and translucent.
Crude oil is one of the three fossil fuels; hydrocarbon-based fuels made from ancient decayed organisms.
It accounts for 40% of the world's energy generation, including 96% of transportation energy!
Formation of Oil
Crude oil is made from ancient aquatic organisms, mostly zooplankton and algae.
Zooplankton refers to small, floating invertebrates.
Algae refers to a large group of aquatic photosynthetic organisms.
When these organisms died, they sank to the seafloor and became buried under sediments. Over time, they were subject to prolonged heat and pressure, gradually transforming into fossil fuels.
Uses of Oil
Once extracted, the compounds in crude oil are separated using a technique called fractional distillation.
You might remember this from GCSE science.
Crude oil is placed in a fractionating column (a tower that's hot at the bottom and cool at the top). The oil evaporates at the bottom of the column and rises upwards as a gas.
Fig. 1 – A simplified diagram showing the process of fractional distillation. Source: StudySmarter Originals
As the gases reach cooler temperatures, they begin to condense, turning back into a liquid. Different molecules condense at different temperatures – the larger the molecule, the higher its boiling point.
Lighter fractions (made of small hydrocarbon molecules) are the most useful as fuels. They're runny and highly flammable. Heavier fractions (made of large hydrocarbon molecules) are less useful as fuels.
Boiling Point (°C)
1 – 4
Feedstock, industrial fuels
4 – 12
32 – 160
Fuel for small vehicles (e.g. boats, cars, motorcycles)
11 – 15
160 – 250
Fuel for jet engines, lubricant, domestic heating, medicine
15 – 19
220 – 350
Fuel for large vehicles (e.g. ships, trains, trucks)
Bitumen for roofs and roads
Petroleum vs Petrol
Petroleum is another term for crude oil – an unrefined mixture of hydrocarbon compounds. On the other hand, petrol refers to a product of crude oil, created by distillation and refining.
Impacts and Effects of Oil Exploration and Extraction
Crude oil is found as a liquid in underground geological formations. It's commonly found in shale formations, a sedimentary rock found in deep marine environments.
What are the different methods that geologist use to locate oil reserves?
Geologists analyse exposed rocks on Earth's surface, and extrapolate below ground. This method provides a reasonable guess, but doesn't account for unexpected folds or faults below the surface.
Drilling a Core
Geologists drill deep cores, stretching thousands of feet below ground. They provide a snapshot of subterranean rock. Drilling multiple cores in an area allow geologists to correlate the rocks, building an image of potential oil reserves. When combined with mapping, drilling is a useful exploratory tool.
A loud sound is directed underground. Unusual reflection or refraction patterns of the sound waves can indicate an oil reserve.
Geologists study Earth's gravitational field. Variations indicate different physical formations, such as oil or natural gas, underground.
Marine mammals, such as whales and dolphins, rely heavily on echolocation (detecting objects using reflected sound). The noise from seismic surveys disrupts their echolocation: impacting feeding, communication, and navigation behaviours.
The majority of oil is extracted using traditional methods, such as drilling and pumping. As it's a liquid at atmospheric temperature, it can flow through wellbores and pipelines.
A wellbore is a hole drilled to aid in extraction and recovery of natural resources, such as oil, gas, and water.
Oil extraction can take place on land, or offshore.
Fig. 2 – A North Sea oil rig. Source: unsplash.com
Drilling for oil damages the landscape, disrupting wildlife and emitting pollution. Offshore drilling carries the risk of oil spills, which destroy aquatic communities.
The BP Deepwater Horizon spill in 2010 caused the deaths of almost 1 million seabirds.
Some oil cannot be recovered using regular drilling and pumping methods, so it's termed unconventional oil.
Oil sands are a mixture of sand, water, clay, and bitumen. They can be upgraded into synthetic crude oil and other petroleum products. However, bitumen is too thick and heavy to flow independently. So, large amounts of earth are removed and mixed with water to become liquid. Then, the mixture is transported via pipeline to a plant, where the bitumen is separated.
Some oil is difficult to extract from its geological formation of origin. So, it is extracted using horizontal drilling or hydraulic fracturing.
Also called fracking, hydraulic fracturing is the high-pressure injection of fluid into a wellbore to create cracks in rock formations. Crude oil will flow through the cracks more freely.
Fracking is harmful for the environment. It has been associated with the release of methane (a greenhouse gas), noise pollution, harmful atmospheric pollutants, and seismic tremors.
Environmental Impacts of Petroleum
Petroleum is a fossil fuel. Like other fossil fuels, it is burned to release energy. This has a negative impact on the environment.
When hydrocarbons are burned, they release carbon dioxide as a by-product.
pentane + oxygen → water + carbon dioxide
C5H12 + 8O2 → 6H2O + 5CO2
Carbon dioxide is a greenhouse gas.
The Earth has a natural greenhouse effect. Without it, it would be too cold for organisms to survive. However, increased concentrations of greenhouse gases contribute to climate change.
Burning fossil fuels accounts for over 75% of global greenhouse gas emissions.
Carbon dioxide isn't the only greenhouse gas produced by burning petroleum-based products. Another by-product is nitrous oxide (N2O). It's only released in small quantities, but it's 300 times more potent than carbon dioxide.
The combustion of petroleum-based products is associated with air pollution. High levels of air pollution can cause smogs, affecting visibility, and impact human health. Individuals with pre-existing respiratory conditions are most at risk.
Sulfur dioxide (SO2) and oxides of nitrogen (NOx) are released into the atmosphere when petroleum is burned. These mix with water vapour in the atmosphere, forming acid rain.
Impacts of acid rain include damage to vegetation, soil erosion, and deterioration of infrastructure.
In a hot, enclosed environment like an engine, the petroleum-based fuel may undergo incomplete combustion. Instead of producing carbon dioxide as a by-product, harmful carbon monoxide and particulate matter are produced instead.
Carbon monoxide is a toxic gas. Ingestion can cause dizziness, fatigue, and loss of consciousness.
Particulate matter impacts human respiratory health. It's also associated with decreased albedo (reflectivity of a surface). When dark particulate matter lands on snow, more radiation is absorbed, thus leading to snowmelt.
I hope that this article has explained oils and fuels for you. Crude oil is a fossil fuel, responsible for 96% of transportation energy. However, extracting crude oil and burning its products has detrimental effects on the environment.
Oil and Petroleum - Key takeaways
- A fuel is a physical substance that can be consumed to produce energy.
- Crude oil (also called petroleum) is a thick, unrefined mixture of hydrocarbon compounds. This fossil fuel is the source of 96% of the world's transportation energy.
- Compounds in crude oil are separated using fractional distillation.
- Crude oil reserves can be located using geological mapping, drilling a core, seismic surveys, or gravimetry. Crude oil is extracted by drilling or fracking.
- When oil-based products are burned, they release greenhouse gases and harmful pollutants.
1. Alexandra Adams, Summary of Information concerning the Ecological and Economic Impacts of the BP Deepwater Horizon Oil Spill Disaster, NRDC, 2015
2. Brett Jameson, Nitrous oxide, a powerful greenhouse gas, is on the rise from ocean dead zones, The Conversation, 2021
3. Gioietta Kuo, When Fossil Fuels Run Out, What Then?, MAHB, 2019
4. S-Cool, Chemicals from Oil, 2021
5. United Nations, Causes and Effects of Climate Change, 2022