Put up for sale last year and facing a possible shutdown, Maine’s largest power plant has been taken off the market.

Wyman Station in Yarmouth had been essentially written off as obsolete and too costly to run. But in the topsy-turvy world of energy supply and demand, the 57-year-old oil-fired generator suddenly appears to be valuable again.

The turnabout is linked to last winter’s below-average cold, when New England’s natural gas pipeline system couldn’t supply all of the region’s power plants. As part of a standby program set up by the region’s electric grid operator, Wyman Station and other oil units stepped up to help keep the lights on.

For competitive reasons, neither the grid operator nor Wyman’s owners will discuss the plant’s operations and finances. But it’s widely assumed that Wyman’s electric output will be vital again this winter because three major power plants in New England are going offline.

Beyond that, Wyman may remain a key player for years. Debate is growing over how to expand the region’s gas pipeline capacity, and whatever the outcome, the solutions will take time.

The future of the power station also is of great interest to Yarmouth, which receives $1 million in taxes from the facility and had begun considering how to redevelop the waterfront site.

The plant’s owner, Florida-based NextEra Energy Resources, declined Monday to discuss details of its decision to cancel the sale. The company did provide a summary of a conference call to investors, in which it recounted conducting a competitive bid process last fall and winter and being dissatisfied with the results. Last winter’s developments in the regional energy market reinforced its view that Wyman was worth more than bidders were offering, the company said.

“While these assets are not called upon to run frequently, they play an important role in supporting the reliability of the electric system, and that has real economic value,” NextEra said.

Wyman Station is a landmark in Casco Bay, with its 421-foot smokestack at the tip of Cousins Island visible for miles.

The plant and a small companion unit in South Portland have a capacity of 822 megawatts and can generate enough energy to power 893,000 homes.

But Wyman Station rarely ran in recent years because it competes with natural gas-fired units in New England. They generate roughly half the region’s power and typically are much cheaper to operate.

That equation changed suddenly last winter.

Heavy demand for gas combined with insufficient pipeline capacity to send gas prices soaring to 10-year highs. That led to a rare price inversion – for much of the winter, wholesale gas was often more expensive than oil.

The results were summarized recently in a report from ISO-New England, the grid operator. It noted that during a cold snap from Jan. 20-24, oil plants generated one-quarter of all electricity; coal plants contributed 8 percent. By contrast, natural gas provided 24 percent. The rest of the electricity came from nuclear plants, and hydropower and other renewable sources.

On the coldest days, ISO-New England reported, very few gas-fired generators were producing power. Much of the gas supply was being used to meet existing contracts for homes and businesses.

“Throughout the winter, much of the oil fleet was running at full capacity, even through the nighttime hours when demand is lower,” the ISO said.

The need for oil and coal generation could be even greater this winter. Peter Brandien, the ISO’s vice president of operations, outlined the situation last spring for federal energy regulators. He noted that the Vermont Yankee nuclear power plant, as well as coal and oil plants in Salem, Mass., will go offline. Those three units generated more power than all the oil-fired units in last year’s standby program.

“Unless the weather is mild, next winter will be more challenging, given retirements,” Brandien said.

That point was reinforced by a spokesman for the Massachusetts Municipal Wholesale Electric Co., which owns a small percent of Wyman’s output on behalf of 12 Massachusetts municipal utilities.

“Natural gas pipeline constraints, particularly in the winter months, are forcing New England to rely more on oil units like Wyman to ensure electric system reliability,” David Tuohey said. “That will continue to be the case until the region builds new gas pipeline capacity for electric generation, which will provide some relief to reliability issues and the economic stress of high and volatile electricity prices.”

The timeline for this new capacity is uncertain. The six New England governors are promoting a large expansion plan that could involve public subsidies, while some private pipeline companies are proposing their own projects. Meanwhile, some environmental groups are fighting gas expansion, saying it will hurt development of wind and other renewable sources.

In Yarmouth, the plant ran frequently 30 years ago and paid roughly half of the town’s total property taxes. Its current $1 million contribution represents 4 percent of the tax base. After negotiations with NextEra, the plant is valued for tax purposes at $50 million, said Nat Tupper, the town manager.

But the tax issue is less important than the future of the 120-acre site and how it might be redeveloped, Tupper said. That dialogue was on the front burner after the sale was announced last year, but now may be put off.

“Property taxes are important, but the most important issue is what’s going to happen to the site,” Tupper said. “What’s the sequel to Wyman Station, if there is one?”