In this report, the modified averaging approach to the solution for the dynamic performance of an externally pressurized, gas-lubricated, circular thrust bearing in a laminar flow regime, is presented under the assumption of a small harmonic vibration. This approach can evaluate the inertia effects under highly unsteady conditions. The accuracy of the approximate solutions presented in a previous report are compared and evaluated under similar conditions and the following conclusions are obtained: (1) The conventional averaging approach, in which all the inertia terms are averaged out across the film thickness, gives a good approximation. (2) The first-order solution of the perturbation method becomes remarkably inaccurate as the unsteadiness becomes high.