The fire on Carnival Corp.’s (CCL) cruise ship Triumph was caused by a leak in a fuel oil return line, the U.S. Coast Guard said.

The U.S. investigation of the causes of the incident and the crew’s response to the fire will last about six months, Lieutenant Commander Teresa Hatfield, the Coast Guard’s Marine Casualty Investigation team leader, said during a conference call with reporters today.

The ship, which left Galveston, Texas, on Feb. 7 with more than 3,100 guests, caught fire Feb. 10 off the coast of Mexico and arrived in Mobile, Alabama on Feb. 14, after being stranded for four days. The Coast Guard will also try to find out why the ship remained disabled for so long, Hatfield said.

As of last week, a total of 14 Triumph voyages through April 13 had been canceled. Carnival, based in Miami, has said the incident will reduce earnings in the first half of fiscal 2013 by 8 cents to 10 cents a share.

To contact the reporter on this story: Kasia Klimasinska in Washington at kklimasinska@bloomberg.net

To contact the editor responsible for this story: Romaine Bostick at rbostick@bloomberg.net