SEATTLE — Several meetings that the Port of Vancouver held in private to discuss a lease for a proposed oil-by-rail terminal should have been open to the public, the Washington Supreme Court ruled Thursday.

Three conservation groups sued in 2013, arguing that the port violated the state open public meetings law when it discussed a lease for the Vancouver Energy project in a series of closed meetings that year.

The port had argued that commissioners met in closed session to discuss issues related to minimum lease price, which was necessary to prevent potential poaching by rival ports.

The Supreme Court unanimously ruled Thursday that a Clark County Superior Court judge erred in ruling in favor of the port and dismissing the claims by Columbia Riverkeeper, Sierra Club, and the Northwest Environmental Defense Center. It sent the case back to the lower court to rule on those issues.

While discussions about the minimum lease price can be held in private, the court said general discussions about the factors influencing that price must still happen at open public meetings.

“The plain language of the provision confines discussion in executive session to the lowest acceptable value to offer land for sale or lease, and does not permit discussion of all factors that influence price,” Justice Charles Wiggins wrote.

It’s unclear how the decision would affect the Port of Vancouver’s lease for the oil-by-rail project that would handle about 360,000 barrels of crude oil a day.

After the groups sued, the port held a new open meeting and a new vote in October 2013 to approve the lease.

“This is a real win for setting a precedent for transparency and public involvement,” said Brett VandenHeuvel, Columbia Riverkeeper’s executive director. “This will stop that illegal practice of excluding the public and lead to better decisions.”

The port said in a statement Thursday that they’re continuing to review the opinion to determine the next steps.

“We expected the Supreme Court to offer further definition of “minimum price,” which is helpful for all municipalities to ensure we continue carrying out our missions with transparency,” the port said in an emailed statement.

Tesoro Corp. and Savage Cos., operating as Vancouver Energy, are proposing a $210 million facility that would receive an average of four 1½-mile long crude oil trains a day, likely traveling on tracks between Spokane and Vancouver. Oil would temporarily be stored on site and then loaded onto tankers and ships bound for West Coast refineries.

A state energy panel is currently reviewing the project. It will make a make a recommendation to Gov. Jay Inslee, who has the final say.

On Wednesday, hundreds turned out to the panel’s hearing about the project’s draft clean-air permit.

Vancouver Energy says it remains committed to building a safe, state-of-the-art facility that will provide jobs and economic value and improve our energy security on the West Coast.

Opponents say the project poses too great a risk to people and the environment, it’s not in the public’s interest and that dangers extend well beyond the facility to include communities along rail lines across the state.