In this paper an overview of the angle based particle swarm optimization algorithm (thetas-PSO) followed by its application to optimal reactive power procurement is provided. Among the ancillary services is the reactive power control, which has an important role in efficient operation of the power systems. Implementing a commercial based structure for reactive power scheduling is the most attractive option in deregulated environments. Here is defined a model which attempts to minimize the cost of reactive power procurement and energy losses which incorporates ordinary technical criteria and voltage stability margin in special as soft constraints. From mathematical points of view, the reactive power market can be formulated as a nonlinear optimization problem. The thetas-PSO, as an extension of the standard Particle Swarm Optimization algorithm, is applied to solve the problem of reactive power market. The IEEE 30-bus test system is used to illustrate the efficiency of this approach. The results are compared with those obtained by standard PSO showing that the thetas-PSO has a good potential to converge to better feasible solutions with few iteration steps.