BILLINGS, Mont. — Montana regulators on Thursday turned back an effort by environmentalists, health advocates and some landowners who sought to force energy companies to divulge more information about fracking chemicals used to produce oil and gas.

During fracking, known formally as hydraulic fracturing, companies pump large volumes of industrial fluids underground to release oil and gas trapped in rock formations.

The Montana Oil and Gas Conservation Board voted unanimously against a petition that would have made companies either disclose details on the chemicals or justify withholding the information.

The board’s action left in place a 2011 state rule that allows companies to conceal the ingredients of chemicals that are considered trade secrets.

A legal challenge to a different aspect of the 2011 rule is pending before the Montana Supreme Court. Some board members said they did not want to start the process of coming up with a new rule while that case is unresolved.

A coalition of landowners, environmentalists and advocates filed the petition in July seeking to strengthen the disclosure rule and make it more like a rule in neighboring Wyoming. They said the current state rule violates the public’s right to know about matters that can threaten public health.

The Montana Petroleum Association argued against changes, saying the public should not have access to proprietary company information.

Several of those who filed the petition urged board members to adopt it during a Thursday public hearing.

Among them was Mary Anne Mercer, a public health practitioner at the University of Washington whose family has a Richland County farm that’s been the site of oil drilling. Although her family has benefited financially from oil production, Mercer worries about the open ponds around the property that are used for fracking wastewater.

Without knowing what’s in the fracking fluids, she said it’s impossible to assess the potential hazard those products pose to water supplies and human health.

“I worry about what may be happening to our land … and the pollution that might be left behind when all this oil has been extracted,” she said.

An estimated 4,000 to 7,000 oil and gas wells have been fracked in Montana, with the practice first seen in the state in 1951, said Jim Halvorson, a petroleum geologist and administrator of the state oil and gas board.

Halvorson said he knew of no cases where fracking directly harmed groundwater. There’s also been “no direct evidence” that the rules in place since 2011 have damaged health and safety, he added.

“We have not heard of an issue,” Halvorson said.

An attorney for the petitioners, Kathleen O’Brien, said the group would review the board’s decision before deciding if they will go to state court to challenge the outcome.