WKBJ waveform inversion of Expanding Spread Profile 5 from the North Atlantic Transect is presented. The inversion consists of a Monte Carlo search to determine the major features of the model, followed by a gradient descent to the global minimum. Nonlinear error analysis completes the analysis. Modifications to existing algorithms to allow the searth for low velocity zones and interfaces are described. The results agree closely down to midcrustal depths with results from trial-and-error inversions. Previous interpretations have concluded that a low velocity zone exists in the lower crust. Our waveform analysis shows that this feature may exist but is not necessarily needed to satisfy the data. ¿ American Geophysical Union 1988