The prospect of oil development in the biologically rich ecosystem of the Arctic National Wildlife Refuge (ANWR, or the Refuge), on Alaska's North Slope, has been a focus of the American energy debate ever since oil was discovered on nearby state lands. At the heart of the debate is a part of the Refuge that has potentially significant oil and natural gas resources and also serves as habitat for numerous species, such as polar bears, caribou, waterfowl, and others. The U.S. Fish and Wildlife Service (FWS), within the Department of the Interior (DOI), manages the Refuge and has periodically updated plans to guide its management. On December 22, 2017, President Trump signed into law P.L. 115-97 , which establishes an oil and gas program in the Refuge's Coastal Plain, to be administered by DOI's Bureau of Land Management (BLM). The ANWR provisions were included in tax reform legislation enacted under the budget reconciliation process. The law requires at least two lease sales (of no fewer than 400,000 acres each) for the Coastal Plain within 10 years and contains provisions for the distribution of revenues and royalties. Surface development is limited to 2,000 acres, which need not be concentrated in a single area. The Congressional Budget Office estimated the state and federal revenue from the first two lease sales at approximately $2.2 billion over 10 years (with 50% of revenues—$1.1 billion—going to the State of Alaska and 50% to the federal government). However, once the areas for lease are determined, and depending on the market conditions at the time of the lease sales, the bids the government receives may be higher or lower. Drilling in ANWR, as elsewhere in the Arctic, is a difficult and expensive prospect. A key factor in what companies may bid for leases is the price of oil, which as of January 2018 is relatively low. After acquiring a lease, companies will have to analyze seismic data and drill exploratory wells to determine where oil may be located and estimate amounts in relation to possible revenues, in order to decide if they want to develop any discoveries and produce oil. In addition to the work on hydrocarbon discoveries, moving oil found in ANWR to market will require infrastructure, most likely new pipelines, to transport the oil to shipping terminals and eventually to refineries. The oil and gas program mandated by P.L. 115-97 is similar but not identical to ANWR oil and gas leasing programs proposed in two other bills in the 115 th Congress, H.R. 49 and S. 49 . These bills contain various provisions related to the program that were not included in P.L. 115-97 , possibly owing in part to limitations imposed by the budget reconciliation process on the matters that can be considered in reconciliation legislation. In addition to conducting oversight of the oil and gas program's implementation, Congress could choose to address some of these other issues—such as issues related to environmental compliance, judicial review, and special management areas within the Coastal Plain—in future legislation, or it could decide that the provisions of P.L. 115-97 provide sufficient guidance for the program. By contrast, two other bills in the 115 th Congress, H.R. 1889 and S. 820 , would establish the Coastal Plain as wilderness, meaning there would be no commercial development, except to meet the minimum requirements for managing the area as wilderness. Such a designation would be consistent with recommendations in the Obama Administration's Revised Comprehensive Conservation Plan and Final Environmental Impact Statement (RCCP) for ANWR, finalized in January 2015. This report discusses the Refuge's legislative history (including Native claims and congressional actions from the 109 th to the 115 th Congresses), energy resources (including relevant market forces and potential oil and gas resources), Native interests and subsistence uses, and biological resources, as well as issues for Congress related to development under P.L. 115-97 . ANWR, established by the Alaska National Interest Lands Conservation Act of 1980 (ANILCA; P.L. 96-487 , 43 U.S.C. §§1601 et seq. ), consists of 19 million acres in northeast Alaska. It is administered by FWS within DOI. Development proponents view its 1.57-million-acre Coastal Plain—also known as the 1002 Area—as a promising onshore oil prospect. According to the U.S. Geological Survey (USGS), the mean estimate of technically recoverable oil from multiple prospects on the federally owned land in the Refuge is 7.7 billion barrels (billion bbl); there is a low probability that more than 11.8 billion bbl could be recovered on the federal lands over the life of the prospective fields. (In comparison, the United States currently uses about 7.1 billion bbl per year; see " Oil Resource Potential .") The amount that can be recovered depends, in part, on the economics of the oil market. When oil prices are high, more oil will be economic to produce; when oil prices are low, less oil will be economic to produce. Since January 2014, oil prices have dropped by almost 40%, going from an average of $94.60/bbl to $60.37/bbl in the beginning of January 2018. For all of 2017, nominal prices ranged from a high of $60.46/bbl to a low of $42.48/bbl. In 2005, in the most recent analysis available on ANWR, when oil was priced at $67.65/bbl in 2017 dollars, the mean estimate of economically recoverable oil on the federal lands in the 1002 Area was 7.1 billion bbl, and there was a small chance that the federal lands could have had more than 10.7 billion bbl of economically recoverable oil. (See box, "Old Geological Data, Old Prices, and New Interest," on use of older data.) In comparison, the single giant field at Prudhoe Bay, Alaska, discovered in 1967 on the state-owned portion of the coastal plain located west of ANWR (shown in Figure 1 ), is now estimated to have held almost 14 billion bbl of economically recoverable oil. The available information and analysis indicates that any ANWR oil would be scattered among multiple smaller fields rather than concentrated in a single large field, which would make development more expensive and potentially expand the area in which any environmental effects might occur. Congress's decision in P.L. 115-97 to open the federal lands on ANWR's Coastal Plain to energy development also opens the Coastal Plain's Native lands, based on current law. (See " Alaska Native Claims Settlement Act " and " Chandler Lake Agreement of 1983 .") In addition, development in the Coastal Plain may make nearby state lands along the coast (already legally open to development) more economically attractive to industry for exploration and development. Together, the federal, state, and Native ownerships likely have multiple individual fields with oil potential. Although only fields on the federal lands would produce federal revenue from bonus bids, royalties, and rents, the 2005 USGS figures show that when state and Native lands also are considered, the mean estimate of economically recoverable oil rises from 7.1 billion bbl to 9.7 billion bbl. In addition, there is a small chance that the three ownership areas might contain more than 14.6 billion bbl of economically recoverable oil (as opposed to the high-end estimate of 10.7 billion bbl for federal lands alone), if oil is priced at $67.65/bbl in 2017 dollars. (See box, "Old Geological Data, Old Prices, and New Interest," for a discussion of the use of old data and old prices, and see section on " Oil Resource Potential " for further discussion of prices.) The Refuge, especially the nearly undisturbed coastal plain, is home to a wide variety of plants and animals. The presence of caribou, polar bears, grizzly bears, wolves, migratory birds, and other species in this wild area has led some to call the area "America's Serengeti." (See " The Biological Resources .") Several species found in the area (including polar bears, caribou, migratory birds, and whales) are offered certain limited protections through international treaties or agreements. In the past there have been proposals that the Refuge and two neighboring parks in Canada join to form an international park, with prohibitions on oil exploration and development. The analysis below discusses the legislative history of the Refuge; the economic and geological factors that have triggered interest in development; the Native interests in the area; biological and environmental quality factors; and ongoing issues for Congress. The balance between oil and natural gas development and the preservation of biological resources of northern Alaska has been controversial for decades, even before Alaska became a state. In 1943, the federal government withdrew all lands on the North Slope (the land north of the crest of the Brooks Mountain Range and between Canada and the Chukchi Sea) by Public Land Order (PLO) 82 to prevent certain types of development. In November 1957, Interior Secretary Fred Seaton filed a document protecting some of those lands (plus some additional lands south of the crest of the Brooks Range) for the benefit of wildlife and migratory birds. Alaska was admitted to the Union in 1959. In 1960, PLO 2214 reserved the 1957 segregated area as the Arctic National Wildlife Range. The PLO withdrew the lands from "all forms of appropriation ... including mining but not the mineral leasing laws," thus leaving oil and natural gas development as a possibility. Despite these withdrawals, not all of the Refuge is owned by the federal government. The history of ANWR (and its energy development restrictions) is intertwined with congressional efforts to settle land claims of Native Alaskans. As part of those efforts, some ANWR property was transferred to Native corporations.