The Air Force has been auditing procurement and supply contracts since 1926. In practice, a wide variety of audit work is performed but the major part of procurement auditing affects two general types of contracts-those of a cost-reimbursement nature and those of a fixed-price nature with price redetermination provisions. It is generally agreed that it is appropriate for the Air Force to verify the validity and propriety of claims for reimbursement submitted by contractors under cost- reimbursement type contracts. Obviously, it is impossible for auditors to perform a detailed audit of all transactions relating to the average Air Force contract, therefore, recognized selective audit methods are utilized to the fullest extent practicable. Certain basic factors which auditors are required to consider are: (1) adequacy and reliability of the contractor's accounting system and related internal controls, (2) previous experience with the particular contractor on Government contracts, and (3) the volume of cost to be audited, i.e., the amount of the claim or the amount of the cost statement in relation to the effort and time to be expended on the audit and in relation to the contractor's other business.