We use data from a small aperture array in southern California to quantify variations in source parameter estimates at closely spaced stations (distances ranging from ∼7 to 350 m) to provide constraints on parameter uncertainties. Many studies do not consider uncertainties in these estimates even though they can be significant and haveimportantimplicationsforstudiesofearthquakesourcephysics.Here,weestimate seismic source parameters in the frequency domain using empirical Green's function (EGF) methods to remove effects of the travel paths between earthquakes and their recordingstations.Weexamineuncertainties inourestimatesbyquantifyingtheresult- ing distributions over all stations in the array. For coseismic stress drop estimates, we find that minimum uncertainties of ∼30% of the estimate can be expected. To test the robustness of our results, we explorevariations of the dataset using different groupings of stations, different source regions, and different EGF earthquakes. Although these differences affect our absolute estimates of stress drop, they do not greatly influence thespreadinourresultingestimates.Thesesensitivitytestsshowthatstationselectionis not the primary contribution to the uncertainties in our parameter estimates for single stations. We conclude that establishing reliable methods of estimating uncertainties in sourceparameterestimates(includingcornerfrequencies,sourcedurations,andcoseis- mic static stress drops) is essential, particularly when the results are used in the com- parisons among different studies over a range of earthquake magnitudes and locations.