We investigate the apparent contradiction between the pressure expressions, or "mechanical expressions," and the van der Waals squared-gradient expressions for the curvature coefficients k/R-0, k, and (k) over bar. We show that, in the context of the mean-field theory discussed, both types of expression are indeed equivalent, with the differences only being caused by the thermodynamic conditions used to vary the curvature. (C) 2000 American Institute of Physics. [S0021-9606(00)50713-2].