One of the most remarkable results to emerge from heavy-ion
collisions over the past two decades is the striking regularity
shown by particle yields at all energies. This has led to several
very successful proposals describing particle yields over a very
wide range of beam energies, reaching from 1 A GeV up to 200 A
GeV, using only one or two parameters. A systematic comparison of
these proposals is presented here. The conditions of fixed energy
per particle, baryon+anti-baryon density, normalized entropy
density as well as percolation model are investigated. The
results are compared with the most recent chemical freeze-out
parameters obtained in the thermal-statistical analysis of
particle yields. The sensitivity and dependence of the results on
parameters is analyzed and discussed. It is shown that in the
energy range above the top AGS energy, within present accuracies,
all chemical freeze-out criteria give a fairly good description of
the particle yields. However, the low energy heavy-ion data favor
the constant energy per particle as a unified condition of
chemical particle freeze-out. This condition also shows the
weakest sensitivity on model assumptions and parameters.