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The seismic reflection method accounts for over 90 percent of the geophysical expenditures for oil and gas exploration. Controlled sources of seismic energy emit signals into the earth which are reflected to the earth's surface by density-velocity contrasts associated with variations in subsurface rock lithology, stratigraphy, and structure. The reflected signals detected on the earth's surface are digitized and computer processed to produce seismograms used for geological interpretation to evaluate the potential for oil or gas reservoirs. Original reflection seismology methods developed nearly sixty years ago utilized explosives for seismic sources. However, the use of earth vibratory sources has increased in recent years. The compressional wave vibrator is discussed giving a description of the electrical-hydraulic method of controlling the applied base plate force. The vibrator efficiency for transduction of hydraulic energy into seismic energy is analyzed in terms of vibrator and earth parameters. Source signal design is achieved through selection of several operational parameters specifying the temporal and spectral properties of the vibrator sweep control. Limitations on vibrator system resolution by the signal detection and registration system are considered. Methods of signal enhancement are applied in the field during data acquisition and in computer data processing. Interpretation of vibrator seismograms is optimized by analyzing the parameters influencing system resolution, understanding their interaction, and then specifying the acquisition and processing parameters which will provide the necessary data quality.