# Crude oil: How energy resides

How ancient sunlight ended up in liquid chemical bonds

Source page: https://www.materialinsights.org/energy/crude_oil/resides/

What this tab covers The physical form in which the energy is held or carried, where it comes from, the chain of transformations that put it there, and how concentrated it is.

Crude oil stores ancient solar energy as chemical bonds in liquid hydrocarbons, cooked from buried plankton and algae. It is the most energy-dense and easily moved of the natural fuels.
 Form Chemical energy in liquid hydrocarbon molecules Origin Fossil solar (ancient marine photosynthesis)

#### How it got there
 Fusion in the Sun Sunlight Photosynthesis by plankton and algae Burial in oxygen-poor mud Kerogen in source rock Heating in the oil window Migration into porous reservoir rock under a seal Crude oil (or bitumen, if degraded near the surface)

#### How concentrated it is

| Measure | Value | Note |
|---|---|---|
| **Crude oil, net calorific value** | 42.3 (range 40.1 to 44.8) MJ/kg^[1](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_1_Ch1_Introduction.pdf) | About 1.6 times bituminous coal (25.8 MJ/kg). |
| **Natural gas liquids** | 44.2 MJ/kg^[1](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_1_Ch1_Introduction.pdf) | Light liquids produced with oil and gas. |
| **Oil shale and tar sands (as mined rock)** | 8.9 (7.1 to 11.1) MJ/kg^[1](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_1_Ch1_Introduction.pdf) | Most of the mass is sand, clay or rock, which explains the large mining volumes. |
| **Oil window temperature** | about 65 to 150 (WSGS) or 90 to 160 (Energy Education) degrees C^[2](https://main.wsgs.wyo.gov/energy/oil-gas/oil-gas-facts/generation) | Sources set the boundaries differently. Above about 150 to 160 degrees C mainly gas forms. |

Plankton and algae that sank into oxygen-poor sea-floor mud escaped decay and became kerogen, a waxy organic solid in shale. Buried 2 to 4 km deep and heated for around ten million years, kerogen cracks into oil and gas. Being buoyant, these migrate upward until trapped beneath an impermeable layer. About 70% of today's oil formed in the Mesozoic era (252 to 66 million years ago).

The resource takes several forms. Conventional oil flows to wells by itself. Tight oil is still held in low-permeability rock and needs horizontal wells and hydraulic fracturing. Oil sands hold bitumen, oil degraded near the surface, which is mined or steamed out. Oil shale holds immature kerogen that must be heated to 'cook' it artificially. At 42 MJ/kg and as a liquid, crude oil is the easiest fuel to store and transport, which is why it dominates transport.

#### Sources

1. [2006 IPCC Guidelines for National Greenhouse Gas Inventories, Vol. 2 Energy, Ch. 1 Introduction (Tables 1.2 and 1.4)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_1_Ch1_Introduction.pdf) IPCC, 2006
2. [How are oil and gas formed?](https://main.wsgs.wyo.gov/energy/oil-gas/oil-gas-facts/generation) Wyoming State Geological Survey, 2024

## Other sections

- [Summary](https://www.materialinsights.org/energy/crude_oil/index.md)
- [Energy overview](https://www.materialinsights.org/energy/crude_oil/energy/index.md)
- [Correlation](https://www.materialinsights.org/energy/crude_oil/correlation/index.md)
- [Abundance](https://www.materialinsights.org/energy/crude_oil/abundance/index.md)
- [Fluctuation in time](https://www.materialinsights.org/energy/crude_oil/time/index.md)
- [Across the Earth](https://www.materialinsights.org/energy/crude_oil/geography/index.md)
- [Impact on nature](https://www.materialinsights.org/energy/crude_oil/nature/index.md)
- [Overview](https://www.materialinsights.org/energy/crude_oil/overview/index.md)
- [Extraction](https://www.materialinsights.org/energy/crude_oil/extraction/index.md)
- [Production](https://www.materialinsights.org/energy/crude_oil/production/index.md)
- [Stocks](https://www.materialinsights.org/energy/crude_oil/stocks/index.md)
- [Cycles](https://www.materialinsights.org/energy/crude_oil/cycles/index.md)
- [Trading](https://www.materialinsights.org/energy/crude_oil/trading/index.md)
- [Movement](https://www.materialinsights.org/energy/crude_oil/movement/index.md)
- [Criticality](https://www.materialinsights.org/energy/crude_oil/criticality/index.md)
- [Characteristics](https://www.materialinsights.org/energy/crude_oil/characteristics/index.md)
- [Emissions](https://www.materialinsights.org/energy/crude_oil/emissions/index.md)
- [Relationships](https://www.materialinsights.org/energy/crude_oil/links/index.md)