41 C.F.R. § 109-40.103-1
(a) Preferential treatment, normally, shall not be accorded to any mode of transportation (motor, rail, air, water) or to any particular carrier when arranging for domestic transportation services. However where, for valid reasons, a particular mode of transportation or a particular carrier within that mode must be used to meet specific program requirements and/or limitations, only that mode or carrier shall be considered. Examples of valid reasons for considering only a particular mode or carrier are:
(b) The following factors are considered in determining whether a carrier or mode of transportation can meet DOE's transportation service requirements for each individual shipment: