Petroleum

Petroleum—commonly called crude oil or just oil—is a naturally occurring yellowish-black liquid mixture found in rock formations. Its main components are hydrocarbons. The term covers both unprocessed crude oil and the refined products made from it.

This fossil fuel formed over millions of years when prehistoric organisms, mostly plankton and algae, decayed without oxygen. About 70% of the world’s oil deposits came from the Mesozoic era, 20% from the Cenozoic, and 10% from the Paleozoic. Conventional oil is usually recovered by drilling, which follows studies of geology, sedimentary basins, and reservoir characteristics. Unconventional sources like oil sands and oil shale are extracted using methods such as fracking.

After extraction, oil is refined—most often by distillation—into many products. These include gasoline, diesel, kerosene, jet fuel, bitumen, paraffin wax, lubricants, and ingredients for plastics, solvents, textiles, refrigerants, paint, synthetic rubber, fertilizers, pesticides, pharmaceuticals, and thousands of other petrochemicals. Global consumption is roughly 100 million barrels (16 million cubic metres) per day. Oil production was a key driver of industrialization and economic growth, especially after the Second Industrial Revolution. Some oil-rich countries, known as petrostates, gained major economic and political influence in the later 20th century by controlling production and trade.

Petroleum is non-renewable, and its use harms the environment, climate, and human health. Extracting, refining, and burning oil releases large amounts of greenhouse gases, overwhelming carbon sinks and making it a major cause of human-caused climate change. Other negative effects include oil spills and air and water pollution at nearly every stage.

Access to oil deposits, along with its price and availability, has sparked domestic and international conflicts, state-backed oil wars, trade disputes, energy policy battles, and other resource struggles. Although production is expected to peak before 2035, a global shift toward renewable energy and electrification—driven by climate concerns—will greatly reduce reliance on petroleum.

**Etymology**

The word *petroleum* comes from Medieval Latin, meaning “rock oil.” It combines Latin *petra* (“rock,” from Greek *pétra*) and *oleum* (“oil,” from Greek *élaion*). The term was first used in monasteries in southern Italy near the end of the first millennium, as an alternative to the older word “naphtha.” It later appeared in manuscripts and books, including German mineralogist Georg Bauer’s 1546 treatise *De Natura Fossilium*. After the oil industry grew in the late 1800s, the word became common for liquid hydrocarbons.

**History**

**Early**

People have used petroleum in some form for thousands of years. Over 4,300 years ago, the Sumerians used bitumen to build boats. A tablet telling the birth legend of Sargon of Akkad mentions a basket sealed with straw and bitumen. More than 4,000 years ago, according to Herodotus and Diodorus Siculus, asphalt (bitumen) was used in Babylon’s walls and towers; oil pits existed near Ardericca and Babylon, and a pitch spring on Zakynthos. In Babylon, petroleum was used for roads, ship caulking, and medicine.

In ancient China, petroleum use dates back over 2,000 years. The *I Ching*, one of the earliest Chinese writings, notes that raw oil was discovered, extracted, and used in China in the 1st century BCE. The Chinese also recorded using petroleum as fuel as early as the 4th century BCE. By 347 CE, oil was produced from wells drilled with bamboo.

In the 7th century, petroleum was a key ingredient in Greek fire, an incendiary weapon used by Byzantine Greeks against Arab ships attacking Constantinople. Persian chemists distilled crude oil, and clear descriptions appear in Arabic handbooks, such as those by Abu Bakr al-Razi. In the 9th century, oil fields were worked near modern Baku, Azerbaijan. These fields were described by al-Razi in the 10th century and by Marco Polo in the 13th, who noted hundreds of shiploads of output. Arab and Persian chemists distilled crude oil for flammable military products. Through Islamic Spain, distillation reached Western Europe by the 12th century. It was present in Romania by the 13th century, recorded as *păcură*.

The Seneca people and other Iroquois in western Pennsylvania dug sophisticated oil pits 4.5 to 6 metres deep as early as 1415–1450. French General Louis-Joseph de Montcalm saw Seneca using petroleum for ceremonial fires and as a healing lotion during a 1750 visit to Fort Duquesne. Early British explorers in Myanmar documented a thriving oil extraction industry based in Yenangyaung.