This paper reports an experimental and theoretical analysis of preferential orientation growth of metallic nanowires during electrochemical deposition using nanochanneled templates. In this work pure Co nanowire arrays were synthesized by electrochemical deposition using porous anodized aluminum oxide templates. The nanowire arrays are found to exhibit near complete preferential single axial orientation. The preferential orientation changed with increasing the applied voltage from hcp, [101-0]hcp, [12-10]hcp to fcc. The observation is explained in terms of nucleation thermodynamics and crystal growth kinetics. The analysis demonstrates that at low applied voltages, when the wire growth is slow, the wire orientation is dictated by the criterion of minimum total surface energy, with the close-packed surfaces forming the external facets of the crystals. At high applied voltages, when the wire growth is fast, the crystal axial orientation is dictated by the growth kinetics, i.e., directions of the fastest growth velocity. These criteria also apply well to the preferential growth of fcc metal nanowires during electrochemical deposition, e.g., Ag, Au, Cu, and Ni.