Working through two winters in the biting arctic cold, roustabouts bored three miles deep into the coastal plain of northeast Alaska in search of oil. In the spring of 1986, they packed up and left, uttering not a word about what they had found and leaving only a short section of steel pipe to mark the spot.

For more than three decades, the findings from the $40 million exploratory well have been one of the oil industry’s most closely guarded secrets. Outside of the oil giants that paid for it, only a handful of people know what was discovered there.

Now the secret has become much more than a curiosity: The Trump administration, undoing decades of environmental protections, plans to sell drilling leases in the area, which is part of the Arctic National Wildlife Refuge and has long been believed to contain North America’s biggest untapped onshore trove of oil.

Anyone interested in drilling in the area urgently wants to know: Was the well — the only one ever drilled there — a dry hole or a potential gusher?

No one will say officially, but The New York Times found an answer in clues hidden 4,000 miles from the Arctic tundra, in the archives of a Beaux-Arts-style courthouse in Cleveland.

“The discovery well was worthless,” said Sidney B. Silverman, a retired lawyer who was involved in a long-since-forgotten lawsuit filed there in 1987.

Mr. Silverman, who is now 86 and divides his time between Long Island and South Florida, reached that conclusion while representing shareholders of Standard Oil of Ohio as it was being acquired by British Petroleum. Both companies had a stake in the Arctic test well and were poised to benefit from further development.

In merger documents, BP had placed only a “nominal” value on the potential reserves in the refuge, and Mr. Silverman and other lawyers suspected that Standard Oil’s shareholders were about to be cheated.

They quickly learned otherwise.

BP allowed Mr. Silverman to conduct a confidential deposition about the well with a BP executive, David Jenkins. Reached by The Times, Mr. Jenkins said his memories were vague, but he recalled the deposition — which was sealed by the court — and telling Mr. Silverman that “there was never any evidence at all, at that stage, that there was anything material within the refuge.”

Mr. Silverman, similarly, remembered being convinced that “either there was no oil and gas there, or the oil couldn’t be produced at an economic value.”

Some of the documents in the case are missing from the court file, perhaps lost over the decades. But in more than 1,000 pages of legal and regulatory filings, The Times discovered other hints that the findings were disappointing. Under oath, a Goldman Sachs banker who worked on the merger testified that BP had led him to believe that the test well results were “not particularly encouraging.”

John Warden, a lawyer who represented BP, said that he had only dim memories of the case but that the well results “became a nonissue.” Told of The Times’s reporting, he added, “It looks to me like you have gotten it right.”

Mr. Silverman hinted at the findings in a memoir he self-published 10 years ago, but has never before spoken out directly about what was said in the deposition. He said he was breaking his silence because of the Trump administration’s decision to open the refuge — protected by Congress for decades — for oil development.

“This is important for the whole country,” he said.

One dry hole does not necessarily mean there is no oil to be found, especially since some decades-old seismic tests indicate that the area may hold as much as 12 billion barrels’ worth. And knowledge of the area’s subsurface geology is valuable. But confirmation that the results of the only test well were discouraging could embolden opponents of drilling and prompt second thoughts among potential lease bidders.

“Knowing that information would help you in an extremely competitive bid,” said Larry Persily, a former federal gas official responsible for Alaska, who noted there had been billion-dollar lease sales in the state. While the well is all but “a pimple on a speck” of the Arctic’s massive landscape, he said, it is a prevailing mystery. “And we love mysteries.”

Oil and gas development in the Arctic refuge, or ANWR — an expanse about the size of South Carolina that is home to caribou, polar bears and other wildlife — has been a goal of Republicans in Congress and many Alaskans for a half-century.

But efforts to open the refuge’s coastal plain, known as the 1002 Area, foundered for years as opponents argued that exploration would irreparably harm one of the country’s largest pristine landscapes.

Republicans saw an opening with the election of Donald J. Trump. In 2017, the Republican-controlled Congress passed a measure to sell oil leases in the refuge. Since then, the Interior Department has moved rapidly to sell leases for the 1002 Area before the 2020 election, when Democrats could regain the White House and block the sales.

The exploratory well was drilled under an agreement among BP, Standard Oil, Chevron and two Alaska Native corporations created to improve economic conditions among the indigenous population. The deal also allowed the oil companies to pursue further exploration on Native lands within the 1002 Area, if the federal government offered leases for the rest of the coastal plain.

At a congressional hearing last week, Richard Glenn, an executive with the Arctic Slope Regional Corporation, one of the Native partners, played down the data’s significance. “You can’t determine the quality of any single basin by one well,” he said.

The corporation declined to comment for this article, as did BP. Chevron said in a statement that the results of its activities in the area remained confidential.

Joe Balash, the Interior Department official overseeing the leasing efforts, told reporters in December that the potential oil riches should attract plenty of interest despite the enduring mystery surrounding the well — a site known as a “tight hole,” an industry term for wells with confidential findings.

“In the oil and gas industry, there’s secrets and then there’s secrets,” Mr. Balash said. “This is the tightest hole, I think, that has ever been drilled.”

A Legal Circus

A year after the exploratory well was completed, a fleet of lawyers descended upon the Cuyahoga County Courthouse in Cleveland. BP, which already held a minority stake in Standard Oil of Ohio, had offered $7.4 billion to buy the rest of it, and the lawyers were there to lodge claims that Standard Oil’s shareholders were being shortchanged.

The deal and the ensuing litigation led to a legal spectacle, with lawyers, executives and bankers shuttling from London to New York, often on Concorde jetliners, and then on to Cleveland and California. The case generated financial headlines around the world.

Eager to distinguish himself from the other lawyers, Mr. Silverman seized on the lack of detail in BP’s offer about what had been found at the test well, known as KIC-1. In a filing, he and his team suggested that the omission had led to a significant shortfall in the value of the deal.

Soon after, BP’s lawyers let Mr. Silverman question Mr. Jenkins, the oil executive. The proceeding was unusually secretive. No copies were made of the transcript, and the original is said to have been stored in a safe at a law firm representing BP.

Mr. Jenkins, who is 80, lives near London and still works in the oil industry, said he had found a notation about the meeting in his 1987 appointment book. He did not remember details of the KIC-1 findings, he said, but recalled that “there wasn’t anything in that well that was particularly encouraging.”

Mr. Jenkins holds out the possibility that there is oil in the refuge. “But not where the KIC well was drilled,” he said.

Mr. Silverman, who ultimately agreed to a settlement, said he had been satisfied by what he learned during the deposition: “I assure you right now that if that property were valuable, if it had any value, I would not have agreed to that merger.”

Mr. Silverman and the other lawyers agreed to a small increase in the offer price and BP stock warrants for Standard Oil’s shareholders, allowing them to potentially share in future profits.

Just as a settlement seemed imminent, lawyers for a large shareholder, the California Public Employees’ Retirement System, known as Calpers, lodged a challenge, also asking whether the price reflected the drilling results.

To allay those concerns, lawyers for Calpers were allowed to see information about the well findings. Yeoryios Apallas, a former California deputy attorney general who represented Calpers at the hearing, said that after reviewing a document that showed details of the test well, he concluded “there was no reasonable basis on which to question the fairness of the price.”

The case was over in about three months. Mr. Silverman and the other plaintiffs’ lawyers shared $22 million in legal fees as they completed one of the era’s largest mergers.

In the decades since, as the debate flared in Congress over whether to open the refuge to oil exploration, Mr. Silverman and others involved in the case quietly kept the secrets of the test well.

“To date, there has been no drilling in ANWR,” Mr. Silverman wrote in his 2009 memoir, “A Happy Life: From Courtroom to Classroom.”

“Environmentalists think their efforts have preserved the wilderness area,” he wrote. “I know better, but must remain silent.”

Keeping the Secret

The oil companies drilling KIC-1 were so concerned about secrecy that, by one industry account, they even shipped the rock cuttings from the well out of Alaska. In 1988, the companies and one of their Native corporation partners sued Alaska to keep the well data confidential.

After a four-year legal battle, the sides reached a tentative agreement that would allow only a few state officials to see the findings. But the state wanted to be sure the data was significant enough to warrant concealing it — that, as the companies contended, it would help in valuing subsurface mineral rights nearby. So, Mark Myers, a state petroleum geologist at the time, became one of the few people outside of BP or Chevron to see it.

In a conference room at BP’s Anchorage offices, Dr. Myers said, he was allowed to comb through the information, which included geological and geophysical data from the well. He was not allowed to take notes. When he finished, he reported only that the findings were significant.

Since then, the state’s files have remained locked away at the Alaska Oil and Gas Conservation Commission in Anchorage. To this day, Dr. Myers, who went on to lead the United States Geological Survey and Alaska’s Department of Natural Resources, and now works as a consultant, has not said whether the results were positive or negative, even as many news reports have speculated about them.

Proponents of opening the refuge to exploration have long cautioned that the KIC-1 findings are only one data point. While no other wells have been drilled within the refuge, many have been drilled near it.

A year after KIC-1 was completed, Tenneco and several partners drilled a well off the coast about seven miles to the northeast. The well was intended not to discover oil, but to learn more about any potential oil-bearing rock formations. The results were not encouraging, according to Douglas R. Choromanski, who helped analyze data from the well, called Aurora.

Other wells have been drilled just west of the refuge, closer to the huge oil field at Prudhoe Bay that spurred Alaska’s oil boom in the 1970s. Some have tapped into significant oil reserves, and some have not.

Dr. Myers said that given new understanding of where oil reserves may be found, much of the focus on the refuge has shifted to the western side, away from the KIC-1 well. A 3-D seismic testing program has been proposed to help pinpoint any oil reserves in the 1002 Area.

A full airing of the KIC-1 findings, though, could come if the Interior Department moves forward with selling leases. Under state rules, lease sales near the well are likely to set off a public release of the data.

In the meantime, the secrecy surrounding the results — and their location — remains a source of gossip, rumor and political intrigue.

In February, Alaska’s new Republican governor, Mike Dunleavy, fired Hollis French, a Democrat on state’s oil and gas conservation commission. In a letter the month before, the governor accused Mr. French of several transgressions, including disclosing to a journalist details of where the KIC-1 files were kept and the protocols for gaining access to them. Mr. French was not accused of revealing the actual data.

At a disciplinary hearing, another commissioner, Dan Seamount, said that after he concluded that Mr. French had divulged the data’s location, “in the dead of night we moved the information to somewhere more secure,” fearing that many people wanted to get to the findings and that “all it would take would be a bulldozer and 15 minutes.” 

“My policy is to tell no one where the data reside, not even what country it resides in,” Mr. Seamount said. “It is arguably the most valuable well information in the world.”