- Using a statistical mechanics bubble competition model, Alon et al. (1994,1995) have shown that the two-dimensional Rayleigh-Taylor (RT) mixing zone bubble and spike fronts evolves as h=alpha (B/S).A.g.t(2) with alpha (B)similar to0.05 and alpha (S)similar to alpha (s). (1+A). The Richtmyer-Meshkov (RM) mixing zone fronts have been found to evolve as h=a(0).t(theta) with different theta's for bubble and spikes. The model predictions were theta (B)similar to0.4 and theta (S) similar to theta (B) at low A's and rises to 1.0 for A close to 1. Full 2D numerical simulations confirmed these scaling laws. Recent experimental results (Dimonte, 1999,2000) have indicated similar scaling laws of the mixing zone evolution, but there were some discrepancies in the values of the scaling parameters, mainly in the value of theta (B) and the similarity parameter, h/< lambda >. It will be shown, based on full 3D numerical simulations, a Layzer type model acid a 3D statistical-mechanics model that these discrepancies are mainly the effect of dimensionality. Accounting for the 3D nature of the problem results in scaling parameters that are very similar to the experimental values. The 3D single mode evolution, used in this model, was confirmed by shock tube experiments.