Expanding spread profiles (ESP's) are spatially localized, wide-angle reflection/refraction surveys using two ships, a multichannel array, and Raydist ranging. The value of the data is primarily the fidelity with which the data are recorded and the mulciplicity of coverage provided by the multichannel array. We feel that the ESP technique has several distinct advantages over other methods of deep crustal studies. These are (1) very accurate range and timing information, (2) fixed and well-known receiver separation (100 m) for accurate phase velocity determination across the array, (3) because of accurate timing and range information, traces from different shots may be used to improve velocity determination (this is limited only by persistence of the particular arrivals), (4) true amplitude recording that allows the use of sophisticated signal processing techniques and tightly constrains models of the observed data, (5) no difficulties with receiver coupling, (6) calibration of charge size changes through overlapping receiver positions, (7) a minimum amount of explosives is required because of the redundancy provided by the multichannel receiving array, (8) minimal deployment and recovery time coupled with low equipment loss rate, (9) 'real-time' data monitoring and analysis to insure the quality of the recorded data, and (10) digital recording in a readily exchangeable standard formant to facilitate the use of digital computers in reducting the vast amount of data acquired. Data of his quality in range, time, and amplitude are required for any detailed inversion or modeling scheme. Dense spatial sampling is required to avoid spatial aliasing, to demonstrate phase coherence between traces, and to observe amplitude variations over short distances. Constant offset profiles (COP's) are fixed range, wide-angle reflection/refraction surveys unsing two ships, a multichannel array, and Raydist ranging. Using this technique, it is possible to develop a profile of refracting type interfaces which are normally absent from the reflection record. With earlier methods, these events are recorded only as 'spot' measurements, and lateral variation is only coarsely determined. Since constant offset profiles are multichannel array measurements at a specific range, variations in velocity, arrival time, and signal amplitude along the profile can be accurately determined. By combining these data with near-vertical incidence multichannel data along the same track, a detailed survey of the deep ocean crust and particularly its lateral variability is possible. This experimental technique is the only method available for a detailed continuous mapping of lateral crustal variations from nonreflecting horizons.