41 C.F.R. § 102-117.75

Shipping—

(a) By land (domestic shipments), use a bill of lading;

(b) By land (international shipments), use of the optional GBL is permitted but not required;

(c) By ocean, use an ocean bill of lading, when suitable, along with the GBL (only for door-to-door movements); and

(d) By air, use a bill of lading.