Performed numerical analysis of co-flowing immiscible liquids in co-axial microtubes investigated the effects of changing the injection velocities and physical properties of the liquids, the interfacial tension and the diameters of the co-axial microtubes on forming disperse droplets in various regimes. The regimes are dripping, transition and jetting. Results, covering a wide range of parameters, identify the conditions for the common boundaries between these regimes. The developed dimensionless correlations, based on numerical results and generated motion picture movies of up to 18 cycles of forming the droplets, accurately predict theses boundaries. Favorable comparisons of present results with those of others and with reported experimental data validate the numerical methodology, the developed flow regimes map as well as the developed correlations for the boundaries between the various flow regimes. These correlations are in good agreement with the present numerical results to within ±10% and with the reported data of experiments used different immiscible liquids to within ±20%. These liquids include ionized water (disperse liquid) and PDMS (Polydimethylsiloxane) oil with R^* = 10, and aqueous solution of glycerine (disperse liquid) and silicone oil, with and without surfactant (Sodium Dodecyl Sulfate) and R^* = 13.8.