If the test is deemed successful, BP is expected to continue the controlled burns as long as the weather conditions are favourable.
The decision to start the test burn came after the US National Oceanic and Atmospheric Administration (NOAA) warned that winds in the area were about to shift and possibly push the oil onto the coast by Friday night.
The oil slick currently has a circumference of about 600 miles (970km) and covers about 28,600 sq miles (74,100 sq km).
The leaks causing it - about 5,000ft (1,525m) under the surface - were found on Saturday, four days after the Deepwater Horizon platform, to which the pipe was attached, exploded and sank.
Workers on a nearby oil platform were evacuated by the US authorities on Monday after the oil slick came dangerously close.
British oil company BP has not been able to activate a device known as a blow-out preventer, designed to stop oil flow in an emergency.
Doug Suttles, the chief operating officer for exploration and production at BP, said it had not yet given up on engaging the valve, but was considering other possible solutions.
These include placing a dome directly over the leaks to catch the oil and send it up to the surface, where it could be collected by ships. This has only been done in shallow water before and is still two to four weeks from being operational.
BP will also begin drilling a "relief well" intersecting the original well, but it is also experimental and could take two to three months to stop the flow.
Forty-nine vessels - oil skimmers, tugboats barges and special recovery boats that separate oil from water - were working to round up oil, BP said.
An investigation has been ordered into the cause of the leak by the interior and homeland security departments.
It will have the power to compel witnesses to testify, and will look into possible violations by the operators of the rig, Transocean.
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