Active control of flow around a circular cylinder at a sub-critical Reynolds number was studied experimentally. The flow was controlled by using a synthetic jet which ran span wise along the cylinder and emanated radially from the cylinder. The experiments were conducted over a two dimensional cylinder in a water tunnel at a Reynolds number of approximately 5800. Seven different jet locations and seven different jet oscillation frequencies were examined. Particle image velocimetry (PIV) was used for flow visualization. The synthetic jet proved to delay flow separation at a wide range of locations and oscillation frequencies. The greatest positive effect on the boundary layer was determined to be when the jet was placed at an angle of 70- to the on coming flow at an oscillatory momentum blowing coefficient at 1.03, and non-dimensional frequency of 0.9. Boundary layer separation was delayed from approximately 90- to approximately 140- and the momentum deficit was reduced by 77-88%.