In a deregulated market environment, the calculation of market power is one of the top priorities of the bodies involved in the market. The bodies generally involved such as the Generation companies (GENCOs), Distribution companies (DISCOs) look towards maximizing profit whereas the RTO/ISOs look to attain a zero market power environment. In this paper, Must Run Share and Nodal Must Run Share (NMRS) is used as an index to calculate market power. To focus upon the fast, accurate calculations and understanding the trends of market power under system changes such as various load conditions, transmission line outage and generator outage, Cubic's Spline Interpolation is used as a technique to interpolate between market powers calculated over a few operating condition set points. A demonstration of the employment of such a system is represented in this paper which will help in achieving the objectives of the players or firms involved in the electricity market. This system will be dynamic enough to suggest the operating conditions for a desired level of market power for any of the above named firms under unexpected system changes. The work is done on IEEE 14 bus test system on the MATLAB version R2012b. © 2015 IEEE.