The factors which influence the performance characteristics of diamond impregnated core bits and roller cone bits are examined, and actual field drilling data are analysed to determine these factors. Methods for selecting the appropriate bit type for optimised drilling are also highlighted. The importance of core drilling to the exploration and exploitation of the earth's natural resources and to the integrity of engineering structures is highlighted. An investigation of the slim hole continuous core drilling system and its application in the oil and gas exploration is analysed. The highly successful integration of oilfield, mining and geotechnical exploration technologies in a special investigation programme includes several elements which are important in the application of slim hole methods for oil and gas exploration are analysed. Many of the technical issues associated with a slim hole approach have been addressed in the development and application of the drilling, and coring equipment and systems. The project has given an opportunity to evaluate the advantages and disadvantages, merits and limitations for applying different drilling and associated technologies for deep hole construction to safety.