Use of a three-dimensional geoscienfific modelling system in offshore sand resources analysis is described. The benefits of a three-dimensional approach to geological modelling are that geologists can concentrate on geological interpretation without the constraints embodied in a two-dimensional approach and geological models can be used directly for aggregate volume assessment, in terms of global and local estimates, with no need to construct isopachytes. An algorithm has been developed which, on the basis of the geological model and variable extraction criteria, yields parameters required for detailed extraction design: depth of dredging, volume of aggregate and ratio of aggregate to waste in the total extracted volume. In addition, the algorithm also accepts as input a three-dimensional geostatistical model of aggregate resource. Data from an offshore site investigated in relation to land reclamation for the Chek Lap Kok Airport, Hong Kong, are modelled, and results are presented for demonstration.