Mont. Code Ann. § 15-35-104

Each coal mine operator shall compute the severance tax due on production for each calendar quarter on forms prescribed by the department. The statement must show the tonnage produced, the average Btu value of the production, the contract sales price received for the production, and other information that the department may require. The completed form, with the tax payment, must be delivered to the department not later than 30 days following the close of the quarter. The form must be signed by the operator if the operator is an individual or by an officer of the coal mine operator if the operator is a business entity. A person operating more than one coal mine in this state may include all of the person's mines in one statement. The department may grant a reasonable extension of time for filing statements and payment of taxes due upon good cause shown.