Cobalt nickel nanoparticles with an oxide shell were prepared by polyol reduction syntheses with varying heating rates, reflux times, surfactants, and reagent concentrations. Differences in particle formation temperature, as evidenced by the reaction medium changing color from violet to black, the UV-Vis absorption spectra of aliquots of reaction media extracted throughout the synthesis reaction, and the colloidal stability of the particle dispersions were observed when the surfactant was changed between otherwise identical reactions. These changes in the reaction kinetics, and therefore the particle sizes of the different samples, also resulted in varying magnetic properties and air stabilities of the samples. Particles with diameters of 15 nm, synthesized using oleic acid, displayed exchange biasing and enhanced coercivity below 50 K, with Hex = 650 Oe and an increase in Hc from 570 Oe to 910 Oe after cooling in field to 2 K. These particles were stable in air over a period of at least five months, showing no change in magnetic moment. Smaller (6 nm) particles synthesized with the same surfactant did not exhibit exchange biasing after field cooling and experienced degradation of their magnetic properties upon exposure to air for one month. Particles synthesized with trioctylphosphine and mixtures of trioctylphosphine and oleic acid were 5 nm and formed the most stable dispersions, but oxidized upon drying in air to non-ferromagnetic phases.