The breakup of the complex drop formed following the collision of a 4 mm diameter drop, failing by gravity into the center of a horizontal 2 mm diameter fluid jet, was investigated. The geometry of the collision was kept fixed; only the jet velocity and the fluid properties, surface tension, viscosity, and density were varied. Thirteen different values of the Ohnesorge number were thus considered, from 0.00.3 to 0.238. The collisions were recorded with a high-speed camera. Dimensional analysis is the tool used to analyze the obtained data, and a new parametric space, Capillary versus Ohnesorge number emerges. The role of viscosity is found to be important during the mixing and deformation stages of the complex drop. An interdependence of the viscosity and surface tension at two different levels in the breakup of the complex drop was also apparent. The results are compared with some previous research for head-on collisions of equal-sized drops and with data from the literature for the breakup of a drop in an airstream. Using the new parametric space, a single unified treatment is proposed for the data on all three breakup phenomena.