Transmissivity and storage estimates are questioned in laterally heterogeneous aquifers as to their representativeness of underlying assumptions in the classical aquifer test methods. For this purpose, the aquifer parameter estimations are obtained by the slope-matching procedure, and their statistical properties are investigated. The change of lateral heterogeneity is obtained with radial distance from the well center. Frequency-and distance-based weighted, harmonic, and geometric averages of aquifer parameter estimations are suggested in addition to the most frequently occurring (mode) estimates. The application of slope method leads to a sequence of aquifer parameter estimations, the arithmetic averages of which correspond to classical type curve match or straight-line results. Because of the lateral heterogeneities in the geological set up, aquifer parameter estimates cannot be constant. DOI: 10.1061/(ASCE)HE.1943-5584.0000614. (C) 2013 American Society of Civil Engineers.