"How do we know this, if you don't mind my asking?"
Government Doubles BP Leak Estimate To 60,000 Barrels Per Day
However, the numbers have changed as the parameters of the well have. Initially, there was the statement that no oil was leaking from the well.
Then the oil started dribbling up out of the wrecked riser and the drill pipe. As the estimates have increased so has the apparent amount of oil. While the former could have been a bit of 'can you top this!?' journalistic sensationalism, there is a very good reason we have seen the change.
When the initial blowout and fire occurred, the flow from the wellbore was limited by the fluid in the riser, the bent pipe, and the relative if imperfect integrity of the plug that was leaking enough to cause the blowout in the first place. I would wager the initial channel(s) throuh that cement plug in the wellbore were relatively small, but as the high pressure formation fluids carry bits of sand, they erode the channel in the cement plug, increasing the size of those channels.
The choke orifice the formation has been producing through, formed by the plug, has been increasing in size, and thus, more oil has been produced on a daily basis as time goes on.
Removing the riser also contributed to the reduction of resistance to flow.
It is tough to measure the flow rate of one fluid into another, and 60,000 bopd is roughly 120% of the production from the best wells known.
Thank you for the link, FRiend.