The conclusion that simultaneous vibroseis recording does not provide adequate signal separation (Martin & Bacon 1993) is, in my opinion, short-sighted, as it takes into account only the individual records. A 30 dB separation cannot be easy to accept by a field geophysicist, but in real field surveys we never use individual records for interpretation.If we take into account the fact that, in 3D surveys, coverage will seldom be below 1200%, if not much higher, and differences in offset and azimuth among interfering sweeps will add to the separation of energy coming from different vibroseis locations, the 30 dB separation will improve considerably and will easily reach 40 or 50 dB. When using up-and-down sweeps, crossover problems can be attenuated or eliminated by choosing sweeps that cross at 50 Hz, where high-line rejection filters are normally present. T h e suggestion of using more seismic lines simultaneously in land acquisition, like multistreamer operations, does not take into account the much higher down-time expected by increasing the number of seismic lines in Europe's highly populated areas.The success of surveys using much worse separation methods in comparison with today's efficient electronics and better understood interference phenomena, demonstrates that the conclusions of Martin's experiment cannot be applied to 3D field surveys without additional investigation of other interference attenuation factors.

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