TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDifferential sticking is one of the major downhole complications encountered in drilling operations. Generally oil base spotting fluids are used to release the stuck ups. However, the results are not always good.Based on sticking severity in the laboratory experiments, differential sticking has been classified into two major categories viz.; normal and extreme differential sticking. Sticking of first category can be released by using conventional oil base spotting technique, however, it fails to release the extreme stuck ups which invariably results in operations like jarring, washover, side tracking etc. and leads to loss of considerable precious rig days, costly drill string and/ or loss of the well.In order to meet the challenges of such extreme stuck ups, a new acid based formulation (Formulation-A) has been developed. It reacts chemically with the cake instantaneously and destroys it. The chemical destruction of the cake leads to the release of both types i.e. extreme as well as normal differential sticking. It has no adverse effect on the properties of drilling fluid and is also non damaging to the drill string.The two case histories i.e. in the deep well no. GGG, TD-2900 m. with horizontal drift of 660 m. in the Geleki field and high drift well no. AAA, TD-1835 m. with horizontal drift 904 m. in Ahmedabad field prove the usefulness and effectiveness of this formulation in releasing more than 7 days old severe stuck ups. Said formulation designed in tune with the expected contact area exhibited excellent results with quick release of stuck ups. This technique has since been widely accepted for the use in extreme cases of stuck ups.