This paper presents a methodology to quantify the economic benefits of having centralized energy market and ancillary services market. A long-term production cost simulation model, which performs security-constrained unit commitment (SCUC) and security-constrained economic dispatch (SCED), is employed to simulate the operating conditions of the system with and without the energy and ancillary services market. The proposed methodology is used in the Midwest Independent Transmission System Operator, Inc. (MISO)'s Value Proposition study, which looks into the value provided by MISO to its market participants and their customers.