An internal BP document released on Sunday by a senior U.S. congressional Democrat shows that the company estimates that a worst-case scenario rate for the Gulf of Mexico oil spill could be about 100,000 barrels of oil per day. The estimate of 100,000 barrels (4.2 million gallons/15.9 million liters) of oil per day is far higher than the current U.S. government estimate of up to 60,000 barrels (2.5 million gallons/9.5 million liters) per day gushing from the ruptured offshore well into the sea.

The document, which is undated, was released by U.S. Representative Ed Markey, chairman of the energy and environment subcommittee of the House of Representatives Energy and Commerce Committee.

The amount of oil actually gushing from the well has been a matter of considerable controversy since the spill began on April 20, with critics saying BP has deliberately understated the flow rate.

"This document raises very troubling questions about what BP knew and when they knew it," Markey said in a statement. "It is clear that, from the beginning, BP has not been straightforward with the government or the American people about the true size of this spill. Now the families living and working in the Gulf are suffering from their incompetence," he added.