Abstract The paper discusses the application of reliability theory to offshore foundation piles. Tire theoretical risk of failure for piles is computed for a range of realistic soil and loading conditions. The reliability analyses are updated in the light of long term field experience and the results used to comment on reassessment procedures for foundations. It is concluded that, if standard design procedures are followed, the outcome is likely to be that, generally, piles in sand are more at risk of failure than piles in clay, and piles governed by the dead load condition more at risk than those for which the extreme environmental load governs. Introduction For almost 50 years, the offshore industry has made use of driven piled foundations to support offshore production facilities. Throughout this period, the design of such piles has remained a constant source of attention, especially with regard to the methodology for predicting the ultimate capacity. An account of how offshore pile design procedures have evolved and in particular those of API RP2A is provided in TooIan and Horsnelll and Pelletier et al'. To date, there have been no recorded incidence in the North Sea of piled foundation failure, with many of the structureshaving experienced their 100 year design storm. McClelland et al.3 in their review of 650 major platforms in the Gulf of Mexico, covering a period of 4000 platform years and seven major storms, including Hurricanes Carla (196 1) and Camille (1969), identified a total of 25 failures, only 3 of which were attributable to soil failure and none to failure of driven piles under axial loading. A more recent study in the aftermath ofHurricane Andrew also indicated that, although there were 150 incidents of damage and failure to platforms, none were attributable to pile failure. The situation is different under sustained loading where McClelland et al report two cases of failure in clay. If the survey is expanded to include pipe piles for marine structures under test load, then Tomlinson4 and Toolan5 have reported failures in sand at well below design capacity. The results of these testsrequired the piles to be redesigned in order to achieve a satisfactory foundation. In frontier areas, pull-out tests on conductors in calcareous soils have indicated much lower frictional resistance than used in design, leading to remedial measures to platform foundations b. Similar problems are known to occur in micaceous sands. Failures have been reported of platform piles which have bee; installed by combinations of jetting, drilling and driving. However since there is no agreed design procedure for such, little can be learnt of general application from hindcast studies, other than to proceed with extreme caution if contemplating using such installation techniques. Another category of ‘pile failure’ arises when the pile becomes unserviceable as a structural element during installation. This may be through buckling, tip damage or fatigue during driving.