PHILADELPHIA - Marvin Odum, president of Shell Oil, was attending a meeting of the parent company's executive committee in Singapore when word trickled in that an exploration well drilled in Alaska's Chukchi Sea - the crowning step in a multi-year $7 billion quest - was a dry hole.

Maybe not bone dry. In a recent interview, Odum wouldn't say. But in the oil business glossary, a dry hole is one that can't pay off commercially, and Shell's hole definitely qualified. The parent company, Royal Dutch Shell, abruptly dropped any further drilling - a setback for the industry, though a relief for environmentalists.

For years, they had fought a vigorous, litigious and politically intense battle over the Chukchi. Meanwhile Shell, lured by potentially rich rewards, had overcome a couple of embarrassing rig mishaps at sea and patiently navigated the courts and the Obama administration's permitting process. Now, geology had rendered its verdict.

Odum, who subsequently announced that he would be retiring at the end of this month, said the news about the well didn't hit all at once, but that the drilling results and analysis came in small, painful drips over several days of the executive committee meeting.

Odum knows all too well the element of chance that drives the oil-drilling business. The mechanical engineer has spent his entire 34-year working life at Shell and has overseen successful exploration in the Gulf of Mexico and elsewhere. (About a third of Shell's capital spending goes to North America.) The tools of the trade have grown more sophisticated over time, with computer-aided seismic surveys that can give exploration companies detailed three-dimensional, multicolored maps of the subsurface. Still, at the end of the day, there is only one way to find out for certain whether oil or natural gas is lurking deep in the Earth.

"Through geology and seismic surveys, we had reduced the risk to where the only way to reduce it more was to put down a well," Odum said, adding that Shell put it "where we thought there was the highest prospect" of a discovery. If they had been correct, Odum said, the reward could have been fields as rich in oil as the Gulf of Mexico, which produces 1.6 million barrels a day worth $22 billion a year, even at today's depressed prices.

"The size of the prize was always big enough to take that next step and find out for sure," he said.

Odum took time to reflect during a recent visit to the University of Pennsylvania's Wharton School. Odum's departure has saddened many at Shell who see him as, well, a nice guy. He says now is a logical time to leave Shell, which hired him on the spot during the one and only job interview of his life. His father also did some work for Shell, devising a specially fitted type of steel pipe that made drilling easier - and which NASA later used, too.

But now, Royal Dutch Shell is undergoing a massive reorganization to gird itself for a more climate-conscious world, but one that Shell says will still need vast quantities of fossil fuels.

With the recent $52 billion acquisition of the British BG Group, Royal Dutch Shell is making liquefied natural gas a bigger part of its future. It also picked up alluring deepwater oil fields off Brazil. It has reorganized its lines of management by function, rather than geography. And it is planning to sell $30 billion in assets over the next three years, twice the normal rate.

That could include some items in North America.

To many analysts, it looked like Odum was pushed into leaving. "He's a very competent guy. Very low key and sure of himself," said Fadel Gheit, oil analyst with Oppenheimer & Co. "But unfortunately for him, the results were pretty bad. It's basically on his watch."

Gheit said the drilling rig mishaps at sea cost hundreds of millions of dollars and, back on the mainland, Shell had to write down the value of shale oil and gas properties. But, he added, these setbacks were "not entirely his fault."

Odum says that while he's not rushing into anything, he plans to find new work in the oil business. He also plans to spend more time with his new grandson, his golf clubs, his cello (an eight-year-old Christmas present he's just learning) and his three motorcycles - a Harley-Davidson, a BMW and a Ducati. "I love riding. It's the engineer in me," he said.

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The night before Odum arrived at the University of Pennsylvania, students from the Penn Sustainability Review, an environmental publication, met to figure out how to pressure the university into selling the endowment's investments in fossil fuel companies.

Last year, 88 percent of Penn undergraduates who voted in a referendum favored divestment from fossil fuels. (A third of undergraduates voted.) Similar measures are sweeping across college campuses, efforts that in some ways resemble the anti-apartheid disinvestment campaigns aimed at South Africa.

Fossil Free Penn, which launched the referendum, has called for the university to stop new investments in the fossil-fuel industry, sell off holdings in the top 200 fossil-fuel companies within five years and reinvest a portion of the funds into renewable energy.

The group estimates that 4 percent of Penn's $9.6 billion endowment is invested in fossil-fuel companies.

Royal Dutch Shell is a big target not only because it produces oil and gas to satisfy global demand, but also because of its record in places such as Nigeria's Niger Delta, where thieves and local insurgents frequently siphon oil from pipelines, sometimes causing leaks or explosions. Community leaders and environmental groups have accused the company of ruining the environment; the company has been selling or reducing its troubled operations onshore and sticking to those offshore.

And in the United States, the push to drill in the Alaskan Arctic drew sharp opposition. Under Odum, "the company consistently demonstrated a lack of preparedness and a willingness to push the limits of the law, technology and common sense," said Michael LeVine, a lawyer with Oceana, which opposes all offshore drilling. "Shell's misadventures in the Arctic Ocean should serve as a cautionary tale for other oil companies considering investments in remote and dangerous places."

If ever the oil industry needed a human face, however, Odum has been it, representing Shell in a coalition that supported the Obama administration's cap-and-trade climate strategy back in 2009.

At Penn, he said the Obama administration's Clean Power Plan - which would favor gas over coal - was "not perfect, but it's a good reasonable place to start" and he was "supportive." He said he would prefer an economy-wide carbon tax if it were ever politically feasible, even though it would raise retail prices of oil products.

"I intellectually understand it," he said during a class in which a student asked about the divestment movement. "If your point is to divest from fossil fuel companies, just be very clear what you want to accomplish. If it's a symbolic move - 'we want to voice our position' - I say, 'fine.' I'd much rather say there is an opportunity here, particularly with companies like Shell, to co-create a solution with a company that deeply understands energy markets."

Odum said, "The idea that you can turn fossil fuels off and other sources on and all will be well in 10 years, it's just wrong."

He said, therefore, that "if you're going down that route [toward divestment], then I would ask you to look at differences between companies out there. I think we're trying to do the right things."

Shell has long basked in a bit of climate-sensitive sunshine because of Odum's revelation (at a Washington Post event) that the company factors in a $40-a-ton carbon price when it does the economic analysis on a new project, an adjustment that would penalize proposals that are the worst from a climate change point of view. Asked about the Paris climate accord, he said "we will never get this transition going at the pace people want without a price on carbon."

A Penn professor had an astute question: Does Shell assign a carbon price only to the energy the company uses to extract oil or gas? Or does it apply the price to the end use on all oil and gas found?

Odum clarified that it applied only to the amount used in extraction - a tiny sliver of the overall climate impact of a project.

Odum deflected a question about whether Shell should use part of its huge annual capital budget, now about $33 billion after the BG merger, to promote renewable energy. He said that shareholders of a company like Shell might prefer if Shell stuck to what it knew - finding oil and gas - and let shareholders take other money and invest it in firms specializing in renewable energy.

Divestment is not the only hot-button issue at the University of Pennsylvania. When Odum arrived earlier in the day at the Wharton School's radio station to do an interview, the producer offered to screen out callers who were particularly irate about shale gas drilling, which has been a huge issue in Pennsylvania, where many residents say wells have contaminated drinking water.

Odum told her not to worry. And when the subject didn't come up, he brought it up himself.

"What's happened in the back yard here in Pennsylvania has changed the world," Odum said of the giant Marcellus gas reserve in the state that has lowered prices and made it possible to replace dirty burning coal-fired power plants with gas-fired ones. But he added, "there is a right way to develop this gas" and then there are the pollution hazards residents worry about. "Those are not difficult problems to solve," he said. Shell is part of a group of companies cooperating with the Environmental Defense Fund to measure potent methane leaks that could negate climate benefits of burning gas instead of coal.

"I come out in favor of very clear, very strong regulations," Odum said. "From the perspective of a company like us, it protects us because everybody then has to do it the right way."

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But most of the students who saw him in a classroom, and later at an open event, zeroed in on business decisions steered by the price of oil, which has tumbled about 70 percent since July 2014. Shell has slashed capital spending to about $20 billion from about $35 billion, and it has shelved its planned Carmon Creek oil sands project in Canada. Instead of exploring for shale oil in two dozen basins, he said the company is down to six "sweet spots."

"We're in a commodity business, and when you're in a down cycle, everything is difficult to decide," he said. "You've got to keep your balance sheet strong. Not just to remain solvent but able to make strategic moves when everyone else is suffering."

When deciding on a project, he said, Shell looks at its economics, its "resilience" if economic conditions go bad, political factors, country risk and environmental issues. He said that before the steep price drop, Royal Dutch Shell had been weighing on six or seven big projects a year, but in the past year had signed off on only two.

"You don't make multibillion-dollar choices lightly," he said, when asked about his toughest decisions.

"I could pick an easy one: Alaska. We spent many billions of dollars exploring off Alaska," he said, "but the final answer comes from the drill bit when the oil that we needed for it to be viable wasn't there."