Mont. Code § 77-3-432
In each oil and gas lease granted by the state under this part, there must be reserved to the state as consideration for the lease a royalty in all oil and gas produced and saved from all lands covered by the lease and not used for light, fuel, and operation purposes on the leased premises, which must be equivalent to the full market value, as ascertained by the board at the date of the lease, of the estate or interest of the state in the lands and oil and gas deposits disposed of under the lease. The royalty reservation must be set by the board but may not be less than 12 1/2% on gas and not less than 12 1/2% on oil or casinghead gasoline for each producing well for the calendar month. The state may share the expense of transporting the oil to the nearest market on a basis proportional to the state's royalty interest in the oil and at a rate per mile acceptable to the department.
§ 77-3-432, MCA