For all their power and profits, the international oil companies are in fact in trouble. They may still be swimming in cash, but no longer in oil. Despite vast investment in exploration and production, these days they generally fail to replace the oil they produce each year with fresh discoveries, or even to maintain current levels of output. Shell's oil production has been falling for six years, BP's seems to have peaked 2005, and this week even the mighty Exxon was forced to admit its output dropped 10% in the first quarter of the year.