This paper first proposes a competitive market structure for reactive power procurement and then develops a methodology for incorporating voltage stability problems into the model. The owners of electric transactions should participate in this competitive framework and submit their own firmness bids in ($/MW) to the Independent System/Market Operator (ISO-IMO). ISO clears the market for reactive energy regarding the value of each transaction and utilization cost of reactive power on one hand, and the impact of transaction amount on the voltage security of the power system on the other hand. Here, the voltage stability margin is incorporated into the power flow equations so that the security of the power system is provided when a sudden change in load occurs. Applying the Karush- Kuhn-Tuker theorem to the proposed OPF-based reactive power market model gives the reactive power to be provided at each generation node and amount of each bilateral transaction allowed for physical operation. To illustrate an interesting feature of the proposed methodology, several case studies are carried out over the IEEE 14-bus test system using the well-known GAMS software (MINOS solver). The results show that the proposed structure can provide an incentive for both generators and consumers to support their own electricity contracts by supplying enough reactive power at each generator or load bus.