Drilling liner technology has become a standard for entering depleted reservoirs in areas of the North Sea and Southeast Asia and interest continues to increase for use of drilling liners to overcome other drilling problems. Marketing analyses have shown that further development of drilling liner technology and application has been rated with high priority. Based on experience gathered during the last five years, this paper covers possible further Drilling Liner applications, new challenges, and requirements for new systems. "Drill and Case" systems will be introduced and benefits shown by means of case histories of jobs carried out in Norway and Indonesia. Introduction Drilling Liner technology seeks to drill and case the well in one run. Over the last five years, typical Drilling Liner runs were carried out in applications where the target depth was just a few meters away, but could not safely be reached with standard drilling bottom hole assemblies (BHA's). Drilling ahead with standard BHA's risked loss circulation, hole collapse and potentially losing the BHA, drill string and hole section. The success of the entire well was dependent on drilling just a few meters ahead. Drilling Liner technology has helped solve these problems in Norway and Indonesia—enabling savings of over 1.0 mm US$ per well. A typical Drilling Liner application occurs when drilling into depleted reservoirs—a situation, which will become more evident and critical in the future. Former drilling technology has required the use of intermediate casing strings and/or set cement plugs as a means to achieve this. Using Drilling Liners, it often takes only a few hours to drill the liner to target depth and overcome existing drilling problems. The Drilling Liner was standardized to enter depleted reservoirs, but questions challenging the use of this system in other applications continue to arise. These new applications include long distance (ERD) drilling, deep water/shallow water flows, unconsolidated sands or time critical unstable formations. Market analysis has shown that further development of "Case and Drill" systems are rated within the top level of desired drilling technologies industry-wide. On the other hand, although existing systems have been on the market for some years, they are sometimes not fully recognized as potential cost savers or problem solvers. Case and Drill Simultaneously. Various liner drilling systems and casing drilling systems are on the market. Figure 1 refers to liner and casing drilling concepts. Using casing drill systems, the operator can change the drilling BHA several times, whilst the casing stays in the hole. Due to the fact that the casing reaches to surface, the BHA can be retrieved with jointed pipe or wire line. Under-reamers or extendible bits enlarge the hole to allow the casing to follow. The casing must be designed to withstand all drilling loads from the bottom of the well up to surface.