The Special Prorate Agreement is a special example of an interline agreement in which the distribution of fees and the settlement of ticket costs between carriers are precisely defined. While a regular interline agreement is a broadly understood agreement between two (or more) airlines that allow for a trip on one ticket, the SPA specifies the terms of financing, distribution and invoicing of the fees paid by the passenger (or the buyer) and paying the money for the ticket to only one of the carriers involved.