Gulf Oil Disaster: How big is the Deepwater Horizon oil disasterl?

The current size of the Deepwater Horizon spill is hard to measure exactly, but attempts can be made to estimate it.

Based on oil flow calculations from the National Oceanic and Atmospheric Administration, Dr Simon Boxall, a marine pollution expert, says a total current spill can be estimated at about 7,000 to 10,000 tonnes of oil. (See factbox below for how this was worked out.)

But such estimates should always carry a caveat, he says, as these can be affected by factors such as the condition of the rig, the well and the quality of information available.

In terms of lives lost (11 workers died in the rig explosion), financial cost and environmental damage, the Deepwater Horizon incident is clearly serious. But it is not one of the world's largest spills in terms of size alone.

In fact, based on the estimate above, it would not register in the largest 50 single incident, offshore oil spills that have occurred worldwide. Even the 1989 Exxon Valdez spill - despite the controversy and coverage - is not in the top 10.

However the potential for damage caused by Deepwater Horizon is apparent when looking at the events of June 1979 in the Bay of Campeche, also in the Gulf of Mexico.

In that spill, the exploratory oil well Ixtoc 1 suffered a blowout and wasn't capped until more than nine months later, having released 461,000 tonnes of oil in total.