Abstract The current American Petroleum Institute's recipe [API RP 2A WSD, Recommended practice for planning, designing and constructing fixed offshore platforms, working stress design. API, USA, 1993.] for calculation of hydrodynamic loads on offshore truss structures is compared with the corresponding North Sea Design Practice, as given by the rules of Det Norske Veritas. Most emphasis is put on the hydrodynamic coefficients and the estimation of design current as these issues are identified to be particularly critical. Use of the updated API (1993) recommendations in which the drag coefficient for roughened cylinders is increased from a minimum of 0·6 (API 1991) to 1·05 (API 1993) and where current is included, could lead to a general increase in the estimated load level on slender offshore structures [Petrauskas, C., Heideman, J.C. & Berek, E.P., Extreme wave force calculation procedure for the 20th edition of API RP 2A. OTC paper 7153, In Proc. OTC 1993, Houston, Texas, 1993, pp. 201–211]. The main emphasis with regard to the impact of the new API recommendations, however, is that a consistent approach is provided to the calculation of 100-yr directional loads. This includes taking into account the effect of marine growth on force coefficients, modifying the wave kinematics for directional spreading, and considering current blockage effects, conductor shielding effects, and joint occurrence of wave height and current (i.e., using the associated current as being representative of the current that would lead to the 100-yr load). It is concluded that a consistent approach, such as that underlying the new API RP 2A (1993) recipe, is preferable to the current North Sea Design Practice [Det Norske Veritas, Environmental conditions and environmental loads. DNV classification notes 30.5, 1001.] in this field, and thus that the North Sea Design Practice should be updated. This relates in particular to selection of hydrodynamic coefficients. Measurement programmes to obtain full scale global force data simultatneously with wave and current data are furthermore recommended.