As vessels become more efficient and shipping demands continue to grow the population explosion of vessels at sea is outdistancing even its famous human counterpart. This increases the risk of accidents, particularly in confluence areas and straits, and to avert future disaster it is important to predict trends in global traffic flows so that appropriate measures may be taken in time. This poses a difficult problem. Due to the diversity of nationalities involved, the autonomy of ships and competitive secrecy, it is only possible to account for the present at-sea ship population within about 16 per cent. Geographical distribution is even more doubtful and predicting changes more speculative still.