In a deregulated environment of power systems, the transmission networks are often operated close to their maximum capacity. Besides, the independent system operator must operate the system to satisfy its dynamic stability constraints under credible contingencies. In this paper, a novel technique based on iterative stability constrained Optimum Power Flow is proposed. Particle Swarm Optimization methodology is employed to maximize the social welfare with consideration of static and dynamic functional operating constraints and Dynamic Loading Margin (DLM) requirements with respect to normal condition and contingencies. New linear Hopf bifurcation (HB) index is used for fast detection of the DLM. Furthermore, since the pattern of load increase is difficult to be predicted in the new market environment, a method for determining sensitive loading direction associated with DLM is proposed. IEEE14 bus test system with both supply and demand bidding are used to illustrate and test the proposed technique.