Alaskans voted in favour of statehood in 1946 and adopted a constitution in 1956. Congressional approval of the Alaska statehood bill in 1958 was followed by formal entry into the union in 1959.

During the 20th century nearly 40 earthquakes measuring at least 7.25 on the Richter scale were recorded in Alaska. The devastating Alaska earthquake on March 27, 1964, affected the northwestern panhandle and the Cook Inlet areas, destroying parts of Anchorage; a tsunami that followed wiped out Valdez; the coast sank 32 feet (9.75 metres) at Kodiak and Seward; and a 16-foot (4.9-metre) coastal rise destroyed the harbour at Cordova.

Oil and natural gas discoveries in the Kenai Peninsula and offshore drilling in Cook Inlet in the 1950s created an industry that by the 1970s ranked first in the state’s mineral production. In the early 1960s a pulp industry began to utilize the forest resources of the panhandle. Major paper pulp mills were constructed at Ketchikan and Sitka, largely to serve the Japanese market. These mills closed in the 1990s because of logging restrictions.

In 1968 the discovery of petroleum on lands fronting the Arctic Ocean gave promise of relief for Alaska’s economy, but the problem of transportation across the state and to the rest of the country held up exploitation of the finds. In 1969 a group of petroleum companies paid the state nearly $1 billion in oil land revenues, but the proposed pipeline across the eastern Brooks Range, interior plains, and southern ranges to Valdez created heated controversies between industry, government, and conservationists. In November 1973 a bill passed the U.S. Congress that made possible construction of the 800-mile (1,300-km) Trans-Alaska Pipeline, which began the following year and was completed on June 20, 1977. As a result, oil flows freely from the Prudhoe Bay oil field on the Arctic coast to the ice-free harbour at Valdez, whence tankers transport it to U.S. West Coast ports.

In 1989 the oil tanker Exxon Valdez ran off course in Prince William Sound, causing the most disastrous oil spill in North American history and inflicting enormous damage on the area’s marine ecology and local economy. A massive cleanup effort was undertaken, but only about one-seventh of the oil was recovered. The issue was resolved when the Exxon oil company agreed to pay a $900 million settlement to the federal and Alaskan governments. Another disastrous oil spill occurred in 2004, when a vessel broke apart in the Aleutian Islands and released about 350,000 gallons (1,320,000 litres) of fuel oil into the ocean. Yet another spill, the largest in the history of the pipeline, occurred in 2006 when a transit pipe at BP’s Prudhoe Bay facility ruptured, spreading more than a quarter million gallons (one million litres) of oil onto the tundra. Those catastrophes, however, opened wider the doors to the debate on preservation versus oil exploitation.

In the early 21st century, declining oil production was a major concern of Alaskans. The issue of whether to drill in the Arctic National Wildlife Refuge, in the National Petroleum Reserve–Alaska, and in the Beaufort and Chukchi seas continued to be hotly debated, and U.S. government policy regarding it flip-flopped between Democratic and Republican administrations. In December 2016 Democratic Pres. Barack Obama issued a pair of memorandums that indefinitely banned oil and gas development in the entirety of the U.S. portion of the Chukchi Sea and the majority of the Beaufort Sea. Roughly a year later the Republican-controlled Congress passed legislation that lifted the longtime ban on oil and gas drilling in the Arctic National Wildlife Refuge, and in January 2021 Obama’s successor, Republican Donald Trump, oversaw the sale of oil-drilling leases in the refuge. Democrat Joe Biden, who replaced Trump in the White House, suspended those drilling leases in June 2021.