Oil companies and traders are storing at least 50m barrels of oil in supertankers in a clear sign of supply outstripping demand as the global economy slows.

The surge in floating storage, – enough to meet France’s oil imports for a month and the biggest since late 2001–, is likely to push the Opec oil cartel, which is due to meet on Wednesday in Oran, Algeria, to make a deeper production cut to reduce stocks. Storing oil in tankers is unusual as it is significantly more expensive than inland.