This is the final report of a two-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project sought to develop and test a three-dimensional pre-stack migration code to run on the Los Alamos CM5. This work was done in collaboration with Texaco. The authors implemented a version of Texaco`s phase-shift with interpolation algorithm on the CM5. The authors also tested the algorithm on the Cray T3D in collaboration with Cray participants. Processing of seismic data is extremely computer and I/O intensive. The authors developed methods for efficiently performing both I/O and computing as appropriate for a large three-dimensional seismic dataset. The result was improved capability to image subsurface structures in the earth. The emphasis was on structures that are beneath salt in the US Gulf Coast, where many oil and gas reserves are known to exist but where identifying them from surface seismic data is currently difficult due to the large impedance contrast between the salt and surrounding strata.