HELENA — A majority of the state Public Service Commission appears poised to vote Thursday to approve NorthWestern Energy’s proposed $870 million purchase of 11 hydroelectric dams — although it’s uncertain what conditions it may impose on the sale.

“I do believe the evidence is strongly in favor, that the benefits [of the purchase] outweigh the risks,” PSC Chairman Bill Gallagher, R-Helena, said Tuesday. “The question then becomes, if we modify [the deal] ... is whether any of those conditions would kill the deal.”

Gallagher and fellow commissioners are scheduled to vote Thursday whether to approve NorthWestern’s proposal to buy the dams from PPL Montana — and charge the cost to ratepayers.

The company’s proposal would increase electric rates for its 340,000 Montana customers by about 6.5 percent, making NorthWestern one of the highest-priced major electric utilities in the region.

NorthWestern has asked the five-member PSC — all Republicans — to approve the deal without any strings attached, saying the purchase gives consumers a long-term, reliable source of electricity that will insulate them from the ups and downs of the market.

Commissioner Bob Lake of Hamilton said Tuesday most questions he had about the purchase have been answered by the company and other experts who testified at a two-week hearing in July, and that he’s “comfortable” with the purchase.

“It gives me comfort that [NorthWestern] is going to be a solid supplier of electricity, at pretty competitive prices,” he said. “I think the people of Montana can get pretty comfortable that we are going to get steady rates with this purchase.”

Commissioner Travis Kavulla said he’s not sure how he’ll vote, and that it will depend whether the PSC approves certain conditions that require NorthWestern to assume some risk on the purchase.

“The [company’s] proposal would take all of the business risk associated with owning the dams and puts it on the shoulders of the consumer,” he said.

NorthWestern announced almost a year ago it had agreed to buy 11 hydroelectric dams and one storage dam from PPL Montana, which bought the dams from NorthWestern’s predecessor, Montana Power Co., in 1999.

MPC sold off the dams to PPL, a Pennsylvania firm, in the wake of Montana’s infamous 1997 utility deregulation law.

Public Service Commissioners Roger Koopman of Bozeman and Kirk Bushman of Billings could not be reached Tuesday.

Koopman’s district includes NorthWestern’s Montana headquarters in Butte, but he hasn’t indicated strongly how he’ll vote on the dam purchase. Bushman has not indicated any opposition to the purchase.

The most outspoken critic of the purchase has been the Montana Consumer Counsel, a state-funded consumer advocacy office. Its experts say any approval of the deal should include conditions that impose risk on the company, such as requiring it to pay for any maintenance costs that exceed current company predictions.

The Consumer Counsel also has asked the PSC to approve a lower profit margin for NorthWestern.

“[NorthWestern’s] request comes at an enormous upfront cost,” Consumer Counsel Bob Nelson wrote in documents filed with the PSC two weeks ago. “There are ways to protect Montana consumers and to ensure that the power produced from the hydro facilities benefit them at just and reasonable rates.”

The company replied last week that it has brought forth “the lowest-cost, lowest-risk alternative” to provide power to its customers, and that it’s in the public interest.

Come what may Thursday, Gallagher said he’ll push the PSC to make a decision and not delay. Interest rates are at historically low rates, which makes it a good time for NorthWestern to finance the purchase, he said.

“If [our vote] is favorable, it will be one that communicates that, if it’s acceptable to NorthWestern Energy, that they execute the purchase on the lowest interest rates possible as soon as possible,” he said