Abstarct: Designing of foundations on rock masses, it is necessary that the rock masses be examined from different aspects. One of the aspects in addition to the settlement and instability, is determination the bearing capacity of rock foundations. Because of high strength and rigidity of rocks, the bearing capacity of rock foundations is more than soil foundations. But factors such as rock mass crush, discontinuities, high weathering, karst cavities, faulting, etc. cause bearing reduced. Due to the establishment of many structures on rock foundation and created problems about instability of structures established on unsuitable rock foundations, today, the necessity of accurate and comprehensive examination of rock foundations and estimation of effective parameters in the bearing capacity of them is very important. Khark Island is one of the most important Iranian oil export terminals. For storaging of crude oil at the highest point of the Khark Island, huge tanks with different capacities in an area about 120 hectares are constructed. Oil storage tanks, especially in critical areas, are very important. In order to have sufficient bearing capacity as well as reducing the subsidence, these tanks required an appropriate foundations. Any deficiency in these rock foundations could be able to make a huge irreparable damages. In these thesis after introducing the rock foundations and its failure mechanisms different approach of bearing capacity determination such as use building codes, experimental methods, analytical and numerical methods will be examined. Then bearing capacity and settlement of rock foundations of crude oil storage tanks at Khark Island determined by various methods. In order to examine discontinuities and weak structural factors, the geological strength index is used. The results of studies show that the discontinuities have great impacts on the bearing capacity of rock foundations. Bearing capacity and settlement of Khark Island are in the allowable limit and is suitable for construction of these tanks.