SAN FRANCISCO (MarketWatch) -- The U.S. Coast Guard and BP PLC over the weekend were testing an oil-skimming vessel that may help remediate some of the damage from the well leaking into the Gulf of Mexico that has created the largest spill in U.S. history.

The modified oil tanker, vessel called "A Whale," arrived in the Gulf of Mexico late in the past week and was being tested for safety and environmental standards before being put into service. It is owned by Taiwan Maritime Transport Co. Ltd.

Test results were expected by Monday, according to media reports.

The "A Whale," billed as the world's largest oil-skimming vessel, is in the Gulf of Mexico to help clean up the BP spill. Reuters

The 900-foot-long ship is billed as the world's largest oil-skimming vessel. Its owners claim the ship can separate 300,000 to 400,000 gallons of oil per day, storing the crude and returning the cleaned water to the Gulf of Mexico.

Two containment ships at the spill site are collecting about 25,000 barrels of oil daily. BP plans to double the capacity with the planned deployment of the Helix Producer by Wednesday, according to a media report.

BP's Macondo well has spewed an estimated 50 millions of gallons of oil, roughly 50,000 to 70,000 gallons per day, into the Gulf since on April 20, when the well blew out and the Deepwater Horizon drilling rig exploded. The rig sank two days later. Eleven workers aboard the rig, owned by Transocean Ltd, RIG, -4.26% are missing and presumed dead.

BP has used a containment cap and connecting line to siphon some of the l oil and natural gas leaking from well pipes a mile below the surface. Some of the spillage has been burned on the surface.

Oil has killed wildlife and rolled up on marshes and beaches from Louisiana to northern Florida.

BP has pledged $20 billion for an escrow account to fund cleanup and compensation for victims. The Obama administration has begun investigations of BP for possible violations of civil and criminal laws.