The reliability of an offshore pile foundation under environmental and static loading depends on the uncertainty in the loads acting on the foundation, the uncertainty in the geomechanical soil parameters and the uncertainty in the method used to estimate the pile capacity. This paper proposes state-of-the-art approaches to estimate the axial pile capacity and to calibrate partial safety factors as a function of a target annual reliability, and provides calculated examples for each approach. The paper discusses the reliability of the API and four existing CPT-based methods to calculate the axial capacity in sand of pipe piles offshore, discusses the motivation for a "Unified" CPT-based approach to design offshore piles and presents the reliability of the new Unified design method for pipe piles in sand. The assessment of the axial capacity of piles is discussed and conclusions are drawn on the reliability of our calculations of the axial pile capacity in sand profiles.