  In this work we extend the applicability of the microcanonical ensemble
simulation method, originally proposed to study the Ising model (A. H\"uller
and M. Pleimling, Int. Journal of Modern Physics C, 13, 947 (2002),
arxiv:cond-mat/0110090), to the case of simple fluids. An algorithm is
developed by measuring the transition rates probabilities between macroscopic
states, that has as advantage with respect to conventional Monte Carlo NVT
(MC-NVT) simulations that a continuous range of temperatures are covered in a
single run. For a given density, this new algorithm provides the inverse
temperature, that can be parametrized as a function of the internal energy, and
the isochoric heat capacity is then evaluated through a numerical derivative.
As an illustrative example we consider a fluid composed of particles
interacting via a square-well (SW) pair potential of variable range.
Equilibrium internal energies and isochoric heat capacities are obtained with
very high accuracy compared with data obtained from MC-NVT simulations. These
results are important in the context of the application of H\"uller-Pleimling
method to discrete-potential systems, that are based on a generalization of the
SW and Square-Shoulder fluids properties.
