Counting oil flow can be a crude science

London

JUDGING the supply of the world's most important commodity often comes down to a good set of binoculars.

In a world of Twitter, iPhones and instant information, determining how much oil is pumped by global producers is a moving target.

It relies on a 50-year-old tanker-tracking system to help offset national interests that can shroud the data in secrecy and deceit.

The problem: competing analysis of that data often results in different outcomes.

The International Energy Agency (IEA) will tell you that the Organization of Petroleum Exporting Countries (Opec) pumped 32.6 million barrels a day in January. Ask the US Department of Energy, and the answer is one million barrels a day less.

While measuring output is always important, it's likely to become even more key after a tentative pact announced last month by Saudi Arabia, Russia and others to freeze output at January levels. At stake is a stubborn price rout that's pummelled economies, markets and comp…