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A simple method is presented for estimating the specific storage of a confined aquifer from an overdamped slug test in a fully penetrating well. This method is based on the quasi-steady flow model developed previously by the authors, simplified to decoupled algebraic equations upon using Hvorslev's estimate of the hydraulic conductivity. The model equations are solved efficiently on a spreadsheet sequentially. The ability of the algebraic method to estimate the specific storage of a confined aquifer is assessed against slug test data from three field cases and against sets of synthetic data generated with the rigorous Cooper-Bredehoeft-Papadopulos method, which is used as reference. The algebraic method estimates the order of magnitude of the specific storage correctly in all three field cases, with two of them arithmetically very close to the Cooper-Bredehoeft-Papadopulos solution, while the hydraulic parameters computed with the numerical quasi-steady solution nearly match the reference values. In the cases of synthetic data, the algebraic method estimates the specific storage reliably when the storage parameter α equals 10−4 and within an order of magnitude when α equals 10−5. [ABSTRACT FROM AUTHOR]