The seismic sources of three contained nuclear explosions in tuff at Pahute Mesa are characterized by applying the moment tensor source representation to near-field accelerometer recordings of the events. Propagation path effects are accounted for in the study by generalized ray calculations for several plane-layered models. Synthetic seismograms generated from the estimated sources model well the distance and azimuthal variations in the data. The moment tensors are dominated by the isotropic component with the absolute ratio of isotropic to deviatoric component varying between 2 and 20, depending on the particular Green's function. The isotropic sources indicate the procedure is a good measure of relative yield while the absolute yield is dependent upon the exact Green's function. Source time functions indicate the possibility of a double-pulse source separated by 1.0 to 1.5 sec. This interpretation is limited by the fact that phase information is the least well-resolved portion of the study. In contrast, the stability of the spectral characteristics, such as corner frequency, high-frequency roll-off, and peak value shows the value of the moment tensor in the frequency domain for yield and discrimination studies.