Both deterministic and probabilistic approaches can be used to establish spinning reserve requirements. It has been proved that determining reserve requirements based on probabilistic approaches results in more economical efficiency. So, a probabilistic security constraint unit commitment problem (SCUC) is used to clear energy and spinning reserve simultaneously and to determine system spinning reserve requirement in this paper. Also, the expected load interruption costs of DisCos are incorporated in the SCUC objective function. IEEE reliability test system (IEEE-RTS) is used to demonstrate the presented model.