Recent trends are not helping the picture. The number of exploration wells drilled in British waters has fallen to an average of 20 per year in the past five years, compared with an average of 35 a year from 2004 to 2008, the Oil and Gas Council said. Those wells have had little success, with fewer than 100 million barrels of oil and gas discovered over the past two years — about 20 percent of what British waters are now producing in a year.

Some analysts say the higher profile that the industry gained in the Scottish independence campaign could help turn things around. “People now realize what is at stake in terms of the economic contribution and the number of jobs supplied by the industry,” said Bob Keiller, chief executive of Wood Group, a global oil services company based in Aberdeen.

Thanks in part to the criticism of Mr. Salmond and pressures from the oil industry, the British government, which some executives say has mainly viewed the business as an automatic provider of several billion pounds of revenue to the Treasury each year, is trying to do something about the declines in exploration and other symptoms of malaise in the sector.

The government is setting up a stand-alone regulator called the Oil and Gas Authority. Headquartered in Aberdeen, the agency is expected to be more proactive than the Department of Energy and Climate Change, which now regulates the business.

More important, in the view of some oil executives, is a government review of a tax system that they say is burdensome, complex and unpredictable. “There are not so many countries in the world that have a worse regime,” said Patrice de Viviès, senior vice president for northern Europe at the French oil giant Total. “In risk and reward balance the U.K. is not well placed.”

Not only are taxes on oil production high in Britain, at about 81 percent of profit from older fields, but rising costs are also a problem. Operating expenses per barrel produced have risen 62 percent since 2011.