The prediction of extreme environmental loading is critical to the assessment of the structural integrity of all fixed offshore installations. In the last ten years significant improvements have been made both in our understanding of the applied loads and our ability to model them. In particular, the importance of the following processes has been highlighted: the effects of nonlinearities beyond second-order on wave crest elevations; and both the occurrence and the effects of wave breaking on kinematics high in the water column. These effects must be included in a long-term assessment of loading. The calculation of which requires the following: a long-term model for the metocean environment; short-term models for wave processes and wave loading; and an assessment of model uncertainty. This paper presents an efficient Monte Carlo methodology through which the long - term distributions can be defined. This has been developed within the LOADS JIP. It utilises the present best practice in long-term metocean modelling, short-term models that incorporate the latest knowledge, and a rigorous assessment of epistemic uncertainties. The paper provides the results of a long-term analysis of crest elevations, kinematics, and loading for a location within the North Sea. It contrasts the findings with historical calculations and discusses the implications.