And so far there have been no confirmed measurements of the flow rate from the uncontrolled well (it's too dangerous to approach). The Australian Greens, in an article published August 29, made this estimate:
...based on information available on average flowrates for similar wells in the region and the company's own data we estimate conservatively that at least 3000 barrels of oil per day are being released from the well.Back in 2002, the Montara-3 appraisal well flowed at a rate of 5,000 barrels of oil per day. And other offshore wells in the same basin have tested at nearly 8,000 barrels per day. So this estimate seems defensible.
At 42 gallons per barrel, that's 126,000 gallons of oil per day. The U.S. Coast Guard defines anything over 100,000 gallons as a "major" spill.
The well blew out on August 21, so as of today (9/11) it's been spilling oil for 21 days (click here for a web-counter tracking this spill). That would mean 2,646,000 gallons have been spilled so far.
The West Triton drill rig is now on the scene after a long trip from Singapore, and is preparing to drill a relief well that will intercept the damaged well so they can fill it with mud to staunch the flow. If all goes well, it will take at least 4 weeks to complete the relief well. That means an additional 3,528,000 gallons will be spilled, for a grand total of 6,174,000 gallons. Six million gallons is more than halfway to an Exxon Valdez-sized spill.