The mixing process of hot primary zone gases with secondary air must be rapid and intense for an advanced low NOX gas turbine based on a rich-burn/quick-mix/lean-burn (RQL) combustor. The injection of multiple jets normal into a confined crossflow is a key technology for this combustion concept. Therefore, an experimental investigation of a nonreacting mixing process of jets in a crossflow was conducted. The jets were injected through one stage of opposed rows of circular orifices into a slightly heated crossflow within a rectangular duct with no annular bypass. All geometries were tested with in-line and staggered arrangements of the centerlines of the opposed jets. Using the analogy of heat and mass transfer the temperature distribution was measured, and from that the mixing rate was determined for parametric variation of flow and geometric conditions. In accordance with the application to RQL combustion, emphasis was put on high momentum-flux ratios with high mass flow addition. The mixing process was found to be minimally affected by mainstream Reynolds number and mainstream turbulence, but significantly influenced by the addition of swirl to the mainstream. Correlations based on the experimental data were developed describing best mixing depending as a function of geometric conditions (duct height to hole diameter ratio, relative spacing of adjacent jets) and jet to crossflow momentum-flux ratio.