A procedure for the joint inversion of regional and teleseismic long-period waveforms for source parameters is presented. Three test cases demonstrate that the inclusion of regional distance seismograms to a data set of teleseismic observations stabilizes the inversion process and adds valuable constraints to the source parameter estimates, particularly when the teleseismic Green's functions are inadequate. The added stability and constraints from regional waveforms can be attributed to the robust nature of regional distance Green's functions, as well as the added coverage of the focal sphere that regional data provide. Singular value decomposition is a useful inversion method that is well suited for this study because is provides a measure of the solution dependence on individual observations.