Scottish nationalists have long argued that being governed from London has deprived their country of its fair share of the wealth from Britain's oil and natural gas fields, which mostly lie in North Sea waters off their shores.
"It's Scotland's oil" was the rallying cry in the 1970s that helped raise the profile of the Scottish Nationalist Party, which now leads the country and is pushing for a vote to secede in the referendum on Thursday. Alex Salmond, the politician leading the separatist movement, has pointed to North Sea energy as the treasure that would help finance an independent Scotland — ensuring that the country could continue the generous public spending, including free university tuition, that he is promising voters.
But North Sea energy revenue — even if the bulk of it went to a stand-alone Scotland, as is expected — would not be sufficient to justify such a big bet on the country's economic future.
The approximately 5 billion pounds, or $8 billion, that the British government received in tax revenue from North Sea energy last year would have been the equivalent of only about 3 percent of the Scottish economy.
Scotland has many other industries working in its favor, including banking and financial services, textiles, whisky and tourism. They would continue to play their parts, although the big banks, Royal Bank of Scotland and Lloyds, have both indicated that they would move their headquarters to England if Scotland secedes, and some other multinationals might be harboring similar thoughts.
While the oil and natural gas industry, and its 225,000 or so Scottish jobs, would remain vital to Scotland for years, the North Sea is no longer the bonanza it once was. Oil and gas production has declined by about two-thirds from the peak of 4.6 million barrels a day in the late 1990s, and tax revenue is declining and too erratic to count on, industry experts say.
Even though some big oil companies have begun venturing farther offshore into deeper waters north of Scotland, the industry opposes the independence movement and might think twice before making the billions of dollars of investments required to bring that oil and gas to the surface. The ever-fluctuating price of oil makes any planning by industry executives, not to mention government treasurers,highly uncertain.
Perhaps the harshest reality check on Mr. Salmond's forecasts has come from Ian Wood, a Scotsman who is the retired founder of Wood Group, a global oil services company based in Aberdeen. He is a widely respected figure in the industry whose work has been used for years by the British and Scottish governments.
"Young people voting this week must be aware that by the time they're in their 40s,Scotland will have little offshore oil and gas production, and this will severely hit our economy, jobs and public services," Mr. Wood wrote on Energy Voice, an industry website. "I have been shocked by the amount of misinformation and spin."
Even in Aberdeen, the former fishing port in northern Scotland that has become one of the wealthiest areas in Britain thanks to its role as gateway to the North Sea, there is an undertone of worry. Oil executives say that production costs have risen sharply because aging platforms and equipment require more frequent and extensive maintenance. Some oil and natural gas fields, they say, are now so depleted and their equipment so dilapidated that they cost more to operate than they generate in revenue.
Some operators, including Chevron, have announced staff cuts in Aberdeen, a rarity in that energy-boom city. Last year, Chevron put under review its most prominent British development— an estimated $10 billion project northwest of Scotland called Rosebank —because of costs.
"This is a vulnerable industry," Barney Crockett, a Labor Party member of the Aberdeen City Council, said in an interview.
The government that winds up in charge of Britain's oil and natural gas will face the task of giving tax incentives and finding other ways to squeeze the remaining oil and gas out of fields that are increasingly expensive to develop,analysts say.
"The opportunities are smaller and more challenging to develop than in the past,"Robert W. Dudley, chief executive of the oil giant BP, the second-largest investor in British waters after Royal Dutch Shell, said in a statement last week urging a no vote. "Future long-term investments require fiscal stability and certainty."
There are two main, diverging views on what Scottish victory would mean for the industry. One is that the Scottish government might pay closer attention, given energy's economic importance to the country.
The other view, perhaps the majority one, holds that a period of uncertainty could hamper the industry since the North Sea is already at a crossroad. If Scotland does vote yes, there would be at least 18 months of transition before the country would be fully autonomous.
"The larger players want things cleared up before proceeding," said Alex Martinos, an analyst in London with Energy Intelligence, a research firm.
There are also doubts about whether a stand-alone Scottish government could afford to give the energy industry the new tax incentives that might be needed to continue production in the North Sea. About 40 billion barrels of oil and gas have been produced from the area since the 1970s. That leaves an estimated 12 billion to 24 billion barrels more, still a sizable amount — but it will be increasingly difficult and costly to extract.
A shrinking, but still important, resource
Ownership of the North Seaoil and gas reserves is likely to be a point of debate between Scotland and the rest of Britain, should Scotland vote for independence. The tax revenue the British government derives from oil and natural gas has fallen in recent years, largely because of declining production in the North Sea. And while new fields are under exploration and development, the fluctuating price of oil helps make future revenue assumptions uncertain.
Mr. Salmond's government says it has no plans to increase the tax burden on the oil industry. But whether it could afford to cut taxes is another question.
Even with better management, oil and gas production is likely to tail off to around a couple of hundred thousand barrels a day by 2050, down from about 1.5 million barrels day now, according to Alexander G. Kemp, professor of petroleum economics at the University of Aberdeen.
Fortunately for the Scottish government, 2050 is a long way off — and the immediate future looks better. Thanks to recent heavy industry investments, Mr. Kemp and others foresee production picking up in the next few years. As a result, the Scottish government is assuming that energy-related tax revenue will recover to the annual range of £6 billion to £8 billion.
But those estimates assume oil prices of $110 a barrel. That could prove too optimistic, as expanding energy production in the United States is putting downward pressure on world prices. Oil prices are hovering around $100 a barrel.
Further weighing on the prospects, the industry's cost of retiring depleted fields and decommissioning old oil platforms is likely to rise, crimping tax receipts. The British government has guaranteed tax relief on these costs. Wood Mackenzie, an Edinburgh research firm, estimates that Scottish fields will cost $9 billion in cumulative tax relief by 2030.
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There is little doubt that managing this decline is going to be the main job of whatever government is in charge. The British government, which has long been something of an absentee landlord for the North Sea, has been spurred to action by the referendum's threat.
Mr.Wood, the oil services expert, recommended this year in a report commissioned by the government of Prime Minister David Cameron that the government establish a powerful new regulator, separate from the bureaucratic Department of Energy and Climate Change, and that it provide incentives, like one in Norway that allows small companies to quickly recover cash for their exploration expenses.The Cameron government has said it would act on these proposals.
Whether it gets the chance to fulfill that promise will depend on Thursday's vote.