  It is shown that the method of lowest order contrained variational (LOCV)
which is based on the cluster expansion theory is a reliable many-body
technique to calculate the nuclear matter equation of states. In this respect
the state-dependence correlation functions and effective interactions which
have been produce by LOCV calculation with the Reid Soft Core and $\Delta
$-Reid interactions are used to estimate the size of higher order cluster terms
such as the effect of three body cluster energy in nuclear matter. We find that
the three-body cluster energy is less than 1 MeV beyond the nuclear matter
saturation density and it has weaker density dependence than our previous
calculation with the state-averaged coorrelation functions and effective
interactions. Finally, we conclude that the LOCV method is good enough to
calculate other propertiesn of quantal fluids.
