The assessment of long-term effects of oil pollution is ultimately a matter of field responses and ecological interpretation. Chronic conditions present much greater interpretative problems than the aftermath of a severe spill because the detection of subtle effects has to be made against the usually unknown scales of natural changes taking place. Examples from various coastal benthic communities illustrate types of biological interactions, different types and degrees of biological stability and the sometimes unpredictable timescales involved. Special attention is drawn to the significance of natural fluctuations in recruitment and to the geographical scales on which these may occur. Have such matters been taken into account in the past? For the future the extreme difficulty that may be involved in detecting subtle deterioration necessitates both a considerable increase in ecological awareness and the directing of work on sublethal effects to those species most amenable to ecological study.