The problem of finding the equilibrium or steady-state composition of a chemical system may be formulated as a constrained extremum problem. One often wishes to compute not only the composition, but also its dependence on the parameters of the system. This sensitivity analysis is done as follows: (1) Convert the problem to an essentially geometric program to circumvent difficulties that arise from the boundary behavior of the original objective function. (2) Write the Kuhn-Tucker optimality conditions. (3) Apply the Implicit Function Theorem. The resulting derivatives of composition variables with respect to parameters incidentally offer a method for solving the original problem. 19 pp. Ref.