To date the estimation of long-term wave energy production at a given deployment site has commonly been limited to a consideration of the significant wave height H, and mean energy period T. This paper addresses the sensitivity of power production from wave energy converters to the wave groupiness and spectral bandwidth of sea states. Linear and non-linear systems are implemented to simulate the response of converters equipped with realistic power take-off devices in real sea states. It is shown in particular that, when the converters are not much sensitive to wave directionality, the bandwidth characteristic is appropriate to complete the set of overall wave parameters describing the sea state for the purpose of estimating wave energy production. (C) 2010 Elsevier Ltd. All rights reserved.