Differences in numerical estimations introduced by various levels of approximations in the formulation of sea loads on ships are presented and commented. Twenty two levels are compared, they range from the rough approximation of the so-called "static wave" to a nonlinear 3D time-domain code. The results mainly focus on extreme loads but direct consequences on fatigue loads are also tackled. (C) 2002 Elsevier Science Ltd. All rights reserved.