. " Q

Costs of drilling depend on the kind of oil and what potential energy the oil possesses by virtue of its initial pressure in its reservoir, and by the amount of dissolved gas it may contain. In many cases the crude may have enough potential energy to permit a well to flow large quantities of oil to the surface without any artificial assistance, such as use of gas or water injection. (This is quite prevalent in oil wells in the Middle East.) But when oil cannot flow unaided, or when the pressure in the reservoir has decreased to a pressure that is too low to be economical, costly mechanisms which lift oil to the ground surface must be employed. Furthermore, low pressure in the reservoir and low gas content generally go together. This kind of crude, therefore, must be handled in a different manner.