Theoretical band and confinement interpretation of electron gas in lowest energy sub-band of quasi- 1D metallic wire have been done. Counter effects have been investigated on electrostatic oscillations (plasmons) determined by the electron density response function. Carrier correlations are treated by incorporating the local exchange-correlation (XC) effects within mean- field approximation. Results obtained are in quantitative agreement with experiments data of Nagao et al. (2006 Phys. Rev. Lett. 97 116802). Variation in both degeneracy and confinement potential cause a clear energy- shift in the electrostatic oscillations accomplished by asymmetry in band effective mass. Resultant massasymmetry is attributed to the greater strength of XC- effects. These contributions turns out to be quite logical in describing the splitting of 1D-bands over ad-hoc spin-orbital splitting idea of Nagao et al. Calculated XC-functionals agreed well with the lattice regularized diffusion Monte Carlo (LRDMC) simulation data (2006 Phys. Rev. B 74, 245427, 2009 J. Phys. A:Math.Theor.42 214021). Competition among XC-functionals and kinetic energy tendencies decides a criterion by satisfying which a metallic quasi-1D wire may undergo an instability at certain critical temperature (Tc).