The resistance of reinforced concrete to fatigue has not been much of a problem for engineers who have faced it only in specific applications such as railroad sleepers or highway pavement slabs. But fatigue is almost inevitably a factor in the huge concrete structures required in modern offshore oil fields. It is possible to have members of a structure for which crack widths instead of compression stresses are used to describe the serviceability conditions in the concrete. The new philosophy leads to greater stress variations in the prestressing tendons and thereby introduces a greater risk of failure due to fatigue. The risk is heightened in offshore structures by the fact that they function in a very corrosive environment. Of all the actions to which offshore structures are subjected, only those due to waves are sufficiently repetitive to significantly affect resistance to fatigue. The force from waves increases more than proportionally to their height. Consequently, the dimensions of offshore structures are determined more by the extreme values of the heights of waves than on the values which can lead to fatigue. The incidence of wave effect must be examined more closely. In most present designs an offshore platform consists of a bulky caisson which distributes the load to the ocean floor. Such caissons are also often used to stock crude oil. Columns that support the deck are made slender so that waves meet the least possible resistance. Under the action of the waves the columns are bent. This bending is usually most critical at their bases, but it also may occur sometimes at the tops where the columns are anchored in the caisson. In these areas flection creates vertical tensile stresses that must be compensated for by vertical prestressing. To minimize risk of corrosion of the steel bars, it is wise to avoid tension in service conditions that correspond to the force of 59 foot waves. In summary, fatigue failure of the elements of offshore reinforced concrete or prestressed concrete structures does not seem to be a matter for great concern since concrete has great resistance to fatigue and the frequency of very high waves is low. However, in certain areas it is wise to provide a waterproofing coating and to either eliminate tensile stresses by adequate prestressing or limit theses stresses in the passive reinforcement.