Two different revenue sources have been used to leverage financing for DBFOM concessions. The majority of existing DBFOM concessions use toll revenues to raise project financing. Since 2009, a growing number of DBFOM concessions have been financed using annual availability payments paid by the project sponsor to the private partner. The financing raised from both of these revenue streams is also often supplemented by grants from project sponsors and other contributions, such as right-of-way or complementary construction projects. These two concession models are discussed in further detail in the following sections.