ABSTRACT The total number of coiled tubing drilling (CTD) jobs worldwide has grown from 4 in 1991 to 11 in 1992 and will probably exceed 25 in 1993. While CTD still represents only a small fraction of the worldwide drilling market, the growth rate indicates CTD is a technology that is rapidly coming of age. This paper summarizes the jobs performed to date and charts the applications in an effort to predict future trends. In addition, one specific case study is presented for a well in Alaska. This well was drilled through tubing and underbalanced, thus saving the cost of pulling the completion tubing and preventing formation invasion damage. Coiled tubing is routinely used for live well intervention; its use allows an accepted, safe method for underbalanced drilling. Underbalanced drilling is appropriate for many mature and depleted field re-entry projects and offers a method of both preventing invasion and increasing productivity while enhancing natural flow and ultimate recovery. In addition, differential sticking is eliminated and penetration rate is greatly increased.