BP PLC (BP, BP.LN) said Friday the amount of oil it's collecting from a massive leak in the Gulf of Mexico has declined since Tuesday to 2,200 barrels of oil a day.

BP spokesman John Curry said the flow collected generally fluctuates. The company will provide details later Friday on the reasons why the rate declined from the rate of 5,000 barrels a day the company said were being collected Thursday.

Curry also said that 15 million cubic feet a day of natural gas are being siphoned through a mile-long tube the company inserted over the weekend into a shattered oil pipe on the gulf's floor.

Pressure grew on BP after the company said Thursday it was collecting as much crude as was officially estimated to be gushing out of a deepwater well, signaling that the spill is therefore larger than previously thought.

The growing spill followed the explosion and sinking last month of Transocean Ltd.'s (RIG, RIGN.EB) Deepwater Horizon drilling rig, which was drilling for London-based BP about 40 miles from the Louisiana coast.