Why the world’s largest oil reserves are actually thick, sticky, and ancient molasses

Nature · Published 3 October 2026 Swipe more like this →

In short: Oil sands are not just a fuel source; they are a geological anomaly. These vast, unconventional deposits consist of sand and water saturated with bitumen, a viscous form of petroleum that behaves like cold molasses. While they hold trillions of barrels of potential energy, extracting this resource is a complex challenge.

The formation of these deposits is a story of tectonic collision. In Western Canada, the rise of the Rocky Mountains created a massive pressure cooker effect, forcing light oil to migrate hundreds of kilometers through sedimentary rock. As this oil approached the surface in northern Alberta, microbial degradation stripped away its lighter components, leaving behind the thick, immobile bitumen found today. A similar, albeit smaller-scale, geological process occurred in Venezuela’s Orinoco Belt, where mountain-building forces also drove oil migration toward the surface.

While the term tar sands is often used, it is technically a misnomer; tar is a human-made byproduct of coal processing, whereas bitumen is a natural petroleum product. Because bitumen is so viscous, it cannot be pumped like conventional oil. Instead, it requires advanced techniques like steam-assisted gravity drainage or surface mining to recover. These methods are energy-intensive and costly, often requiring a higher breakeven price than conventional crude. In 2019, Rystad Energy identified oil sands as the most expensive significant oil-producing region globally.

The environmental and economic stakes are immense. Producing crude from these sands generates significantly higher greenhouse gas emissions—roughly 31% more—than extracting conventional oil. Despite this, production has surged, particularly in Canada, where technological advancements have turned the Athabasca, Cold Lake, and Peace River deposits into a cornerstone of national energy output. While Venezuela possesses comparable reserves, political and economic instability have hindered its development, allowing Canadian production to dominate the North American market.

The history of bitumen use stretches back 40,000 years, from Neanderthals using it as an adhesive for tools to ancient Mesopotamians waterproofing reed boats. Today, however, the industry faces intense scrutiny. Critics and scientists have raised alarms over the ecological footprint of large-scale mining and tailings ponds. As the world balances energy security against the climate impact of unconventional fuels, the future of these massive, stubborn deposits remains a subject of fierce debate.

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