A constant-head test, keeping the buildup or drawdown constant in the test well, is aimed at determining the aquifer parameters. A skin zone around the wellbore due to well drilling or completion has diverse property to the aquifer. Five parameters including the transmissivities and storage coefficients for each of the skin and aquifer zones and the outer radius of the skin zone are determined via the simulated annealing approach to describe the flow system with a finite-thickness skin. Estimated results indicate that analyzing the single-well responses, i.e., test-well flow rate and observation-well drawdown data separately, is insufficient for obtaining accurate estimates for skin and aquifer parameters. Analysis of specific drawdown in an observation well gives biased results in the negative-skin case. The skin and aquifer parameters appear to be accurately determined when the flow-rate and drawdown data are analyzed sequentially or simultaneously.