UPDATE 3-BP captures even more leaked Gulf oil on Wednesday

* Capture rate of leaking BP oil continues to increase

* BP working to nearly double surface processing capacity (Updates with latest oil capture figure)

By Kristen Hays

HOUSTON, June 9 (Reuters) - BP Plc (BP.L) (BP.N) said its containment cap system at the site of a Gulf of Mexico oil leak captured about 7,920 barrels (332,640 U.S. gallons/1.26 million liters) of oil in the first 12 hours of Wednesday.

If that rate continues, BP could capture nearly 15,900 barrels (667,800 gallons/2.53 million liters) for the 24-hour period -- the highest per-day amount since the system was installed last week.

The total amount collected since June 4 reached 64,444 barrels (2.7 million gallons/10.25 million liters) with Wednesday's half-day tally, according to BP figures.

The top U.S. official overseeing the operation said earlier on Wednesday that as the capture rate ramps up, BP is working to nearly double the capacity to handle it at the surface.

U.S. Coast Guard Admiral Thad Allen said at a news conference in Washington that BP is working to increase processing capacity at a drillship and a service rig at the water's surface to 28,000 barrels (1.18 million gallons/4.45 million liters) a day to handle the load as the company ramps up the collection rate from the seven-week-old leak.

"If we get this thing to 28,000 barrels a day, that's where I want to be," Allen said.

The collection rate has slowly ramped up since British energy giant BP installed the system last week. On Tuesday, BP said the system captured 15,010 barrels (630,420 gallons/2.39 million liters).

U.S. government scientists have estimated the leak to range from 12,000 barrels (504,000 gallons/1.9 million liters) to 19,000 barrels (798,000 gallons/3 million liters) a day, with one estimate as high as 25,000 barrels (1.05 million gallons/3.97 million liters) a day.

Allen said that team is revisiting its data to try to reach a more solid estimate of the leak's flow rate.

"I'm not going to declare victory or anything until I have hard numbers," Allen said on Wednesday.

The containment cap, placed atop the gushing well pipe a mile (1.6 km) below the ocean surface, is being used to funnel some of the escaping oil and gas from the bottom of the Gulf of Mexico to the surface to be collected in ships and taken away.

Even with the containment system in place, large amounts of oil continue to spew into the ocean. The spill is causing an economic and environmental disaster along the U.S. Gulf Coast.

The system is BP's most successful effort so far to corral the leak, which began after Transocean Ltd's Deepwater Horizon drilling rig exploded and sank in April, killing 11 workers.

OFFLOADING OIL

Initially BP said that Transocean's vessel Discoverer Enterprise, the drillship that is receiving the collected oil, had a processing capacity of 15,000 barrels (630,000 gallons/2.38 million liters) a day. Allen said on Wednesday that this figure was "conservative" and its maximum processing capacity is 18,000 barrels (756,000 gallons/2.86 million liters)a day.

Another ship on Wednesday began offloading oil from the Enterprise to transport to shore, BP said. BP spokesman Jon Pack said he did not know where the oil would be shipped. Texas and Louisiana are home to 43 percent of U.S. refining capacity.

BP can add another 5,000 to 10,000 barrels (210,000 gallons/795,000 liters to 420,000 gallons/1.59 million liters) a day of capacity with a service rig, called the Q4000, that was used for the company's failed "top kill" effort to smother the leak last month, Allen said.

That rig is being hooked up to seabed equipment that will, as planned, pull oil and gas from a failed blowout preventer and enhance the containment cap system.

The Q4000 should be in place next week, Allen said.

However, the Q4000 has no storage capacity, Pack said. The seabed system is expected to divert up to 5,000 to 10,000 barrels a day to the surface, but that oil will be burned off with equipment BP is retrofitting for that purpose, Pack said. (Editing by Will Dunham and Eric Walsh)