PPPs-particularly brownfield concessions involving tolls-have been criticized for trading potentially more valuable future toll revenue for up-front payments, essentially shortchanging the public sector over time.63 The higher cost of non-tax-exempt private financing and the need to provide a return on investment also may result in higher overall financing costs for the private sector. These costs then must be repaid through lower up-front payments to the public sector and/or higher tolls.64 On the other hand, it is argued, in this kind of PPP the private sector also assumes the risk of potentially lower-than-expected toll revenues, while the public sector may benefit from the potential indirect effects of asset monetization (see Monetization of Existing Assets on page 9). Concerns about lost revenue have been addressed partly through careful asset valuation (see also Principle 8) and revenue-sharing agreements, in which the public sector receives a portion of ongoing revenues from the facility (see Glossary).