Petroleum geophysical exploration in the Free World, consisting of seismic, gravity, ground magnetic, and other nonairborne geophysical methods, declined 10.0 percent over 1961. This is the sharpest in the continual series of declines that began in 1957 and amounts to a loss of 1,008 crew-months; it is 32 percent down from the peak year of 1956. Airborne magnetometer activity, on the other hand, rose from 347,841 line-miles in 1961 to 433,473, an increase of 25 percent.

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