The grand-canonical ensemble Monte Carlo method has been used to study
the interfacial tension in a rare-gas film confined to a slit pore wh
ose plane-parallel walls comprise rigidly fixed similar rare-gas atoms
. In narrow pores, where both walls strongly influence the whole film,
the interfacial tension is shown to be a highly complex function of p
ore width and transverse alignment of the walls. Oscillations in the t
ension are correlated with the addition of new fluid layers, the most
highly structured layers corresponding to maxima in the tension. Separ
ate interlayer and intralayer contributions to the tension are defined
and shown to be useful in explaining the physics of the change in the
interfacial tension with the addition of new layers to the film.