Alaska holds some of the largest petroleum deposits in the United States, but the total amount of oil beneath the state depends heavily on which category you’re counting. Proved reserves, the oil companies have confirmed they can extract profitably with existing technology, represent only a fraction of the picture. Federal geological surveys estimate that billions of additional barrels sit in formations that have never been drilled, from the National Petroleum Reserve to the contested coastal plain of the Arctic National Wildlife Refuge. Understanding how much oil Alaska truly has means sorting through these overlapping categories, each carrying different levels of certainty and accessibility.
What Prudhoe Bay Tells Us About Alaska’s Oil History
Any discussion of Alaskan oil starts with Prudhoe Bay, the largest conventional oil field ever discovered in North America. Found in 1968 on the Arctic coastal plain, the field originally held an estimated 25 billion barrels of oil in place. Since production began in 1977 through the Trans-Alaska Pipeline System, the 800-mile conduit running south to the port of Valdez, Prudhoe Bay alone has yielded roughly 13 billion barrels. Total North Slope production across all fields has exceeded 17 billion barrels over the past five decades.
At its peak in 1988, Alaska was pumping about 2 million barrels per day, making it the top oil-producing state in the country. That output has fallen dramatically since then. Today the state produces somewhere around 400,000 to 500,000 barrels per day, and the Trans-Alaska Pipeline runs at well below its design capacity. Prudhoe Bay is a mature field now, its easy oil long extracted. The remaining production comes increasingly from satellite fields and newer developments across the North Slope, but none approaches Prudhoe’s original scale.
Alaska’s proved reserves, the category tracked by the U.S. Energy Information Administration, sit in the range of a few billion barrels. That number shifts year to year as new wells are drilled, technologies improve, and oil prices change what’s economically viable to extract. But proved reserves are a conservative figure by design. They capture only what operators have demonstrated with reasonable certainty they can produce under current conditions. They leave out the enormous volumes of oil that geologists believe exist in formations that haven’t been explored, as well as deposits that are known but not yet profitable to develop.
Billions of Barrels Beneath the National Petroleum Reserve
The National Petroleum Reserve in Alaska, or NPR-A, sprawls across roughly 23 million acres of the western North Slope. The federal government set this land aside a century ago specifically because of its suspected oil potential, but it has seen far less development than the Prudhoe Bay area to the east. That’s changing. Recent geological assessments have revealed that the reserve holds far more oil than previously thought.
In 2017, the U.S. Geological Survey estimated a mean of 8.7 billion barrels of undiscovered, technically recoverable oil in just two rock formations within and around the NPR-A, the Cretaceous Nanushuk and Torok formations. The agency described these estimates as significantly higher than previous assessments, driven by recent oil discoveries in the area that turned out larger than geologists anticipated.1U.S. Geological Survey. Assessment of undiscovered oil and gas resources in the Cretaceous Nanushuk and Torok Formations, Alaska North Slope, and summary of resource potential of the National Petroleum Reserve in Alaska, 2017 The same assessment estimated 25 trillion cubic feet of associated and nonassociated natural gas in those formations.
These are not proved reserves. “Undiscovered technically recoverable” means the USGS believes the oil is geologically there and could be extracted with current technology, but nobody has drilled wells to confirm it yet. Still, these numbers are significant. For context, 8.7 billion barrels is comparable to the total amount of oil produced from the entire North Slope over the past two decades. The Willow project, approved by the federal government in 2023 and operated by ConocoPhillips within the NPR-A, represents one of the first large-scale efforts to tap these resources, though its projected output covers only a slice of the total estimated volume.
The Arctic Refuge and Its Controversial Oil Estimates
No piece of Alaskan land generates more debate about oil development than the 1002 Area, a 1.5-million-acre strip along the Arctic coast within the Arctic National Wildlife Refuge. Congress has argued over whether to allow drilling there for decades. The geological assessments, while now more than 25 years old, suggest the area holds a substantial amount of oil.
The USGS estimated in 1998 that the 1002 Area contains a mean of 7.7 billion barrels of technically recoverable oil spread across ten geological plays. The economically recoverable portion was smaller. Using a conservative threshold of 512 million barrels as the minimum commercially viable field size, the agency estimated about 2.6 billion barrels could be profitably developed in the undeformed portion of the area, distributed among roughly three fields. An additional 600 million barrels might exist in a single field in the more geologically complex deformed zone, though the greater distance from existing infrastructure would make development costlier.2U.S. Geological Survey. The oil and gas resource potential of the Arctic National Wildlife Refuge 1002 area, Alaska
The assessment methodology relied on defining ten petroleum plays and estimating the probable size and number of accumulations within each, filtering out any deposits smaller than 50 million barrels of oil in place as unlikely to be economic on the remote North Slope.3USGS Fact Sheet. Arctic National Wildlife Refuge, 1002 Area, Petroleum Assessment, 1998, Including Economic Analysis These estimates have not been formally updated, so they represent the best available federal assessment even though drilling technology, oil prices, and infrastructure costs have all shifted considerably since 1998. Lease sales in the 1002 Area have attracted limited industry interest in recent years, and the political status of drilling there continues to swing with each administration.
Heavy Oil on the North Slope
Beyond the conventional resources, Alaska sits on enormous deposits of heavy and viscous oil that are far harder to extract. Formations like the Ugnu, West Sak, and Schrader Bluff on the North Slope contain billions of barrels of oil that is too thick to flow easily through rock or through pipelines without special treatment. Estimates for these heavy oil zones range widely but commonly cite 20 billion barrels or more of oil in place. The catch is that conventional drilling and pumping methods recover only a small fraction of this oil.
Researchers have been experimenting with enhanced recovery techniques to make these deposits viable. Recent laboratory work on the Ugnu formation tested a combination of liquid carbon dioxide injection and low-salinity water flooding in an alternating pattern. This hybrid approach achieved a cumulative recovery factor of about 84%, doubling what a standard low-salinity waterflood could manage on its own. As a side benefit, roughly a quarter of the injected COâ‚‚ stayed trapped in the rock, suggesting a potential pathway for carbon storage alongside oil production.4Petroleum Science. Experimental investigation of hybrid enhanced oil recovery techniques for Ugnu Heavy Oil on Alaska North Slope
Other experiments have explored solvent-assisted polymer flooding, where chemical solvents are injected to thin the oil and polymers are used to push it more efficiently through the formation. A laboratory study testing five different enhanced recovery methods on North Slope viscous oil reported recovery factors between roughly 80% and 92%, with the improvement driven by oil swelling and reduced viscosity during solvent injection, followed by better sweep efficiency from subsequent polymer or low-salinity water floods.5Geoenergy Science and Engineering. A laboratory investigation of CO2 influence on solvent-assisted polymer flooding for improving viscous oil recovery on Alaska North Slope These are laboratory results on small rock cores, not field-scale production numbers, so the gap between what works in a lab and what works across miles of frozen subsurface formation remains large. But they point toward a future where Alaska’s heavy oil deposits might contribute meaningfully to production if the economics ever line up.
What Lies Offshore
Alaska’s petroleum potential doesn’t stop at the coastline. The continental shelves of the Beaufort and Chukchi Seas are underlain by thick sedimentary basins that geologists have long recognized as promising. The petroleum resource potential of Arctic continental shelf basins along the North American margin is considered well established in geological terms, though the deeper waters of the Arctic Ocean’s abyssal plains are thought to hold only a minor share of the total.6GeoScienceWorld. The Arctic Ocean Region: Sedimentary basins and petroleum resource potential of the Arctic Ocean region
Federal assessments have at various times estimated billions of barrels of undiscovered oil in Alaska’s offshore federal waters, with the Beaufort and Chukchi Seas together representing one of the largest unexplored petroleum provinces in the country. But offshore Arctic drilling is extraordinarily expensive and logistically brutal. The drilling season is compressed by sea ice, storms are severe, the nearest deepwater port is hundreds of miles away, and any oil spill in icy waters would be far harder to contain than in temperate seas.
Several major oil companies pursued offshore exploration in the Chukchi Sea during the early 2010s, with Shell investing billions of dollars in exploratory drilling before abandoning the effort in 2015 after disappointing well results and mounting costs. Other companies followed Shell’s exit, and major U.S. banks subsequently announced they would no longer finance Arctic oil and gas projects. The offshore resource base is real in geological terms, but the economic and political barriers to developing it are steep enough that no company is actively pursuing large-scale production there today.
Source Rocks and Shale Potential
The oil that fills Alaska’s conventional reservoirs migrated there over millions of years from deeper source rocks, layers of organic-rich shale that generated petroleum under heat and pressure. These source rocks themselves may hold oil and gas that never migrated, trapped within the tight pores of the shale. The shale revolution that transformed production in the Lower 48 states, unlocking oil from formations like the Bakken and Permian Basin through horizontal drilling and hydraulic fracturing, has prompted interest in whether similar techniques might work on the North Slope.
Several source rock formations underlie the North Slope, including the Shublik Formation, the Kingak Shale, and the pebble shale unit. Geochemical studies of samples from dozens of wells and outcrops show that these rocks vary considerably in organic richness. The pebble shale unit averages about 2.4 weight percent organic carbon, while the Shublik Formation averages about 1.7% and the Kingak Shale about 1.5%.7Alaska North Slope Oil-Rock Correlation Study. Alaskan North Slope Petroleum Geochemistry for the Shublik Formation, Kingak Shale, Pebble Shale Unit, and Torok Formation The type and maturity of the organic matter also varies geographically. The Shublik grades from mixed marine and terrestrial organic matter in the west to higher-quality marine kerogen near Prudhoe Bay. Maturity increases to the south, where deeper burial has cooked the organic matter further.
USGS researchers have developed methods to map source-rock potential using well log data, finding that the Kingak Shale shows increasing potential from north to south across the North Slope, with the best zones located at the toe of ancient sediment slopes.8U.S. Geological Survey. Modified method for estimating petroleum source-rock potential using wireline logs, with application to the Kingak Shale, Alaska North Slope Whether any of these formations could support commercial shale oil production remains an open question. The Arctic climate, remote location, and lack of the dense well-pad infrastructure that makes shale development work in Texas or North Dakota mean that even a geologically promising shale play would face economic hurdles found nowhere else in the U.S. oil patch.
Permafrost, Pipelines, and a Warming Arctic
Everything about oil production in Alaska depends on infrastructure built on frozen ground. The North Slope sits atop continuous permafrost, soil and rock that has remained below freezing for thousands of years. Roads, drilling pads, pipelines, and processing facilities all rely on that ground staying frozen and stable. Climate change is eroding that assumption.
Warm oil flowing through a buried pipeline can thaw the surrounding permafrost, weakening the soil and causing the pipe to settle unevenly. When different sections of a pipeline cross different ground types, the resulting differential settlement can bend the pipe and, in severe cases, lead to breakage or leaks. This has already caused problems for certain segments of the Trans-Alaska Pipeline System, where severely thawed permafrost damaged the pipeline’s stability.9Cold Regions Science and Technology. Rapid permafrost thaw under buried oil pipeline and effective solution using a novel mitigative technique based on field and laboratory results Engineers have deployed various cooling technologies, including thermosyphons that passively extract heat from the ground, to stabilize permafrost around critical infrastructure. But as Arctic temperatures continue to rise, these mitigation measures face an ongoing and intensifying challenge.
The warming climate also shortens the winter construction season on the North Slope. Heavy equipment and supply convoys traditionally travel across frozen tundra on ice roads, which can only be built and used when the ground is sufficiently frozen to bear the weight without damaging the fragile surface. Warmer winters mean fewer days when ice roads are usable, squeezing the window for exploration drilling, construction, and maintenance work.
Environmental Footprint of North Slope Development
Five decades of oil production at Prudhoe Bay have provided a real-world record of what large-scale Arctic oil development does to the surrounding environment. Monitoring data show localized impacts to air and water quality, though regulated discharges have remained below limits set to protect human health and ecosystems. About 2% of the land surface in developed portions of the oil field has been physically altered by roads, pads, and facilities.10Environmental Toxicology and Chemistry. Of measured risks: The environmental impacts of the Prudhoe Bay, alaska, oil field
Wildlife populations have been a particular focus of concern. Some unavoidable habitat loss has occurred within the oil field and along pipeline corridors, as expected. But monitoring has shown that no species experienced a measurable population decline due to development. Most wildlife continued to use oil field habitat for breeding, nesting, and summer foraging. The Central Arctic caribou herd, which calves near the Prudhoe Bay area, grew roughly sevenfold from when oil field development began in the early 1970s through the study period, suggesting that habitat was not limiting the herd’s growth even with incremental losses to industrial infrastructure.10Environmental Toxicology and Chemistry. Of measured risks: The environmental impacts of the Prudhoe Bay, alaska, oil field Offshore, the gravel causeways built to support oil operations showed only small, localized effects on water circulation, with low probability of significant negative effects on fish.
These findings come with caveats worth noting. The Prudhoe Bay environmental data reflect conditions through the early 1990s, and the cumulative effects of continued development, combined with a rapidly changing Arctic climate, may alter the picture. The 2% land disturbance figure also understates the broader footprint in one sense: road networks, noise, and human activity can affect animal behavior across a wider area than the physical structures alone. And the caribou data, while encouraging, represent one herd in one location. Extrapolating those results to a different ecosystem like the Arctic Refuge’s coastal plain, which serves as the primary calving ground for the Porcupine caribou herd, requires caution.
Why Companies Keep Leaving
Despite the geological abundance, the trajectory of industry investment in Alaska has pointed steadily downward. Shell walked away from its multi-billion-dollar Chukchi Sea exploration program in 2015. BP, which had operated in Alaska for six decades, sold its entire Alaska portfolio in 2020. Several major U.S. banks announced they would no longer finance Arctic oil and gas projects. The pattern is clear: even as geological surveys continue to reveal enormous resource potential, the combination of high costs, regulatory uncertainty, environmental risk, and shifting corporate climate commitments has pushed many large players away from the state.
What remains is a smaller group of operators, some of them Alaska-focused independents, who see opportunity in the space vacated by the majors. ConocoPhillips, the largest remaining operator on the North Slope, is moving forward with the Willow project and continues to explore the NPR-A. Santos, the Australian company that acquired Oil Search’s Alaska assets, has pursued development in the Pikka unit near the central North Slope. These projects will add production, but none is on the scale needed to reverse the long decline from Prudhoe Bay’s peak.
Alaska’s oil story is ultimately one of geological wealth bumping against practical constraints. The oil is there, in quantities that dwarf most other U.S. states. Between proved reserves, federal resource estimates for the NPR-A and Arctic Refuge, heavy oil deposits, potential shale resources, and offshore basins, the total volume of petroleum that might exist beneath Alaska’s land and waters could easily exceed 50 billion barrels in various categories of recoverability. Whether the world’s appetite for that oil, and the economics and politics of extracting it from one of the harshest environments on Earth, will ever align to bring most of it to the surface is the question that has defined Alaska’s petroleum industry for decades and shows no sign of a clean resolution.