Preservation of a fossil oil reservoir is actually decided to whether the fold neutral plane keeps entirely or not. In Tarim Basin, although the residual cores of Palaeozic anticlines that are greatly denuded still have large geological space, the strata located at the upper neutral plane (UNP) which are favorable to hydrocarbon accumulation could not been preserved easily. The cause of drill failures in Fang-1 and Tadong-3 anticlines is analyzed as cases. In these anticlines, the UNP strata are mostly denuded and only a small part of it is remained. The reason of drill failures is that either well was just drilled to the lower neutral plane(LNP) which belongs to the hydrocarbon-draining area under tectonic compression stress. Therefore, drill risks will be faced to alike anticlines. It is necessary to look for the Paleozoic reservoirs at UNP in anticlines where the strata are less denuded. Besides, an attention should be paid to the Meso-Cenozoic structural and/or lithological reservoirs at LNP in synclines.