Mont. Code Ann. § 75-10-724

Any person who receives notice under 75-10-711, who is held jointly and severally liable under 75-10-715, or who initiates a voluntary cleanup under the provisions of 75-10-730 through 75-10-738 may bring a private right of action, including a claim for contribution or declaratory relief, against any other person who is liable or potentially liable under 75-10-715 for the recovery of remedial action costs. In resolving contribution claims, the court shall allocate remedial action costs among the liable persons based on the factors set out in 75-10-750.