Mont. Code Ann. § 39-71-2107

Within 30 days after the happening of an accident where death or the nature of the injury renders the amount of future payments certain or reasonably certain, the employer shall make a deposit or give security, as herein defined, with the department for the protection and guaranty of the payment of such liability in such sum as the department may direct. However, if sufficient securities are already on deposit with the department or if the department determines that the employer has sufficient financial responsibility to meet the liability of the employer, together with other liabilities already accrued, no such additional deposit or security shall be demanded.