W ell NOK is a vertical exploration well which located on field NNF ofBalikpapan region, East Borneo. This well was drilled in order to producing thehydrocarbon of crude oil on the anticline layer “Y”. In this research whichconducted by writer, casing design is the main topic discussion inspected (in thiscase in form of evaluation) by calculating the installed casing grade in the well thenensure that the installed casing grade is proper to run. The NOK well uses a casingwhich is commonly used in drilling, namely surface casing, intermediate casing,production casing. The parameters that will be taken into account are the pressurethat comes from outside (collapse), the pressure that comes from inside the casing(burst) and tension. The method used to calculate the pressure acting on the casingis the maximum load. The calculation results on this casing are based on the safetyfactor of the company where the nominal of the safety factor burst is 1.0, collapse1.0 and tension 1.3. The results of optimization on the casing calculation obtainedthe results of surface casing of 13 3/8“ H-40 48 ppf having a safety factor collapseof 2.3, a burst of 1.8, and a tension of 5.4. It can be concluded that on the casingsurface 13 3/8“ is able to withstand the pressure of the well because it has meet thesafety factor standards in the company. At the intermediate casing 9 5/8“ H-40 36ppf the results of the casing calculation have a safety factor collapse of 1.4, a burstof 1.3, and a tension of 2.6. It can be concluded that at the intermediate casing 133/8 is able to withstand the pressure that can cause damage because it has met thesafety factor standard in the company. And on the casing liner 7 “K-55 26 ppf theresults of the casing calculation have a collapse safety factor of 1.7, a burst of 1.2and a tension of 2.7. In the 7 “liner case no optimization is done because it meetsthe safety factor standards in the company