Code of Federal Regulations Title 30. Mineral Resources § 30.800.5 Definitions

(1) A cash account, which shall be the deposit of cash in one or more federally-insured or equivalently protected accounts, payable only to the regulatory authority upon demand, or the deposit of cash directly with the regulatory authority;

(2) Negotiable bonds of the United States, a State, or a municipality, endorsed to the order of, and placed in the possession of, the regulatory authority;

(3) Negotiable certificates of deposit, made payable or assigned to the regulatory authority and placed in its possession or held by a federally-insured bank;

(4) An irrevocable letter of credit of any bank organized or authorized to transact business in the United States, payable only to the regulatory authority upon presentation;

(5) A perfected, first-lien security interest in real property in favor of the regulatory authority;  or

(6)Other investment-grade rated securities having a rating of AAA, AA, or A or an equivalent rating issued by a nationally recognized securities rating service, endorsed to the order of, and placed in the possession of, the regulatory authority.