In the modern U.S. history of public-private partnerships, the prevailing project delivery models have been the toll concession and the availability payment contract. In both cases, the private party raises equity and debt financing and takes responsibility and risk for completing design, constructing and providing long-term operations and maintenance. The major difference between the two is that in the toll concession the private party takes the revenue risk and secures its debt with project toll revenues, while the public owner takes the project revenue risk under an availability payment contract and gives a contract covenant to pay that becomes the security for the private party’s debt and return on equity.