We demonstrate the development, testing and application of statistical models to study actual billings (net of discounts) for expedited freight services. The models reveal the structure of net tariffs. They enable carriers to identify customers whose revenues are deficient considering services rendered, and terminals where revenues are deficient considering their mix of business. The models thus point to situations where business activities, pricing structures or negotiated discounts need review. The models also verify that the overwhelming determinants of monthly charges to shippers are the fundamental cost drivers for the industry, namely number of shipments, weight of shipments, and distance shipped.