The development of a rectangular jet of fixed aspect ratio issuing into a rectangular duct was studied. This is a specialized case of jets in crossflow (JICF) of interest in manufacturing processes. The jet is confined in the spanwise and cross-stream directions and the mass flux ratio between the two streams is high. The particular emphasis of this paper is on the asymmetric states that develop as the flow evolves. A Mie-scattering-based technique was used to make scalar concentration field measurements. A full factorial test matrix was employed in order to investigate the relative effects of three parameters: jet to crossflow velocity ratio, injection angle, and downstream distance. An increasingly pronounced asymmetry in the scalar concentration field was found in the 30° and 48° injection angle cases, and worsened for injection angles greater than 48°. These results, combined with laser Doppler velocimetry measurements, showed that the primary flow structure, the counter-rotating vortex (CRV) pair was asymmetric. No asymmetries were found in the inlet or boundary conditions of the experiment. Furthermore, perturbations, such as introducing small skew angles were unsuccessful in altering the basic character of the asymmetry. This leads to the conclusion that this flow geometry preferentially produces asymmetric flow fields. The high degree of confinement is believed to make the flow more prone to the asymmetric states than unconfined JICF.