Conditions for Use. Sole source procurement is not permissible unless a requirement is available from only a single vendor. The determination as to whether a procurement shall be made as a sole source shall be made by the procurement officer, and approved by the Director. The determination and the basis for it shall be in writing. The Service may not award a contract to a sole source before the Director's approval. Confidential Services. The Service may enter into a sole source contract to retain the confidential services of a contractor: To advise the Service in connection with threatened or pending litigation; or For appraisal of real property contemplated for acquisition by the Service.