In the case of an operation PFI contract involving fixed, unitary payments, it is possible to let bidders propose the duration of the contract as part of their bids. Instead, in a concession contract where tariffs are used, the length of the concession could be endogenously determined using the Least Present Value of Revenue (LPVR) method. Once the project delivers an amount of revenue equal to the LPVR submitted by the winning bidder in the tendering process, the contract expires automatically. Then, unexpected variations in service demand are accommodated by changes in the duration of the concession.