Since 1982 over 300 Top Drive systems have been installed worldwide, on virtually every type of drilling rig. An ongoing debate centres on the prime moverfor rotating the drill pipe. Should it be "electric" or "hydraulic"?

The purpose of this paper will be to provide a detailed comparison of both systems, outlining the advantages and disadvantages of both. Details of the designs, installation requirements, efficiencies, actual field performance and relative cost comparisons to install and operate will be presented.

The results presented will showthe relative merits of each system and technically compare the overall operational aspects of each system as reflected in the current drilling environment we are experiencing today. The data presented will provide the potential user with the necessary information to evaluate an application and select a system.

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