By whom?? Seems to me I've seen plenty of numbers, most of which are around 10,000 bpd. Certainly ANY number is going to be somewhat of an estimate, but BP and the Coast Guard are in the best position to make the best estimate. You certainly will never know by "looking for plumes"
Nor is the exact size of the spill known with any certainty. Scientists have said that calculating the size of the spill carefully will be critical in order to predict the amount of damage the oil and chemicals could do in the ocean and onshore in the near term and in the future.So what is the flow rate? Is it 5,000 barrels a day, as BP and the government have repeatedly claimed in recent weeks? Or is it closer to 80,000 or 100,000 barrels a day, as some independent analysts have guessed based on footage of the oil gushing out of the riser pipe?
http://www.energyboom.com/policy/flow-rate-remains-critical-unanswered-question-bp-oil-disaster
In addition, no one knows how long it will continue - even the slant hit is not a sure bet (which is why they're drilling two, it could take four or more tries, months away).
This is a huge field under a mile of water with no sure end in sight. No one can say today "This spill is X barrels."