  The Microcanonical Ensemble computer simulation method (MCE) is used to
evaluate the perturbation terms $A_i$ of the Helmholtz free energy of a
Square-Well (SW) fluid. The MCE method offers a very efficient and accurate
procedure for the determination of perturbation terms of discrete-potential
systems such as the SW fluid and surpass the standard NVT Canonical Ensemble
Monte Carlo method, allowing the calculation of the first six expansion terms.
Results are presented for the case of a SW potential with attractive ranges
$1.1 \le \lambda \le 1.8$. Using semiempirical representation of the MCE values
for $A_i$, we also discuss the accuracy in the determination of the phase
diagram of this system.
