  Within the coexistence region between liquid and vapor the equilibrium
pressure of a simulated fluid exhibits characteristic jumps and plateaus when
plotted as a function of density at constant temperature. These features
exclusively pertain to a finite-size sample in a periodic box, as they are
washed out in the bulk limit. Below the critical density, at each pressure jump
the shape of the liquid drop undergoes a morphological transition, changing
from spherical to cylindrical to slab-like as the density is increased. We
formulate a simple theory of these shape transitions, which is adapted from a
calculation originally developed by Binder and coworkers [{\em J. Chem. Phys.}
{\bf 120}, 5293 (2004)]. Our focus is on the pressure equation of state (rather
than on the chemical potential, as in the original work) and includes an
extension to elongated boxes. Predictions based on this theory well agree with
extensive Monte Carlo data for the cut-and-shifted Lennard-Jones fluid. We
further discuss on the thermodynamic stability of liquid drops with shapes
other than the three mentioned above, like those found deep inside the
liquid-vapor region in simulations starting from scratch. Our theory classifies
these more elaborate shapes as metastable.
