Investigators in Qatar are trying to determine what caused a breakdown that has halted about a third of the country''s liquefied natural gas output, as reported by the Associated Press. The Qatargas I plant has been shut since January 8 because of a "mechanical failure," according to an official, who spoke on condition of anonymity, citing company policy. He did not say when supplies would resume. The plant is operated by a consortium led by state-owned Qatar Petroleum and has an annual capacity of 10 million tons. Energy giants Exxon Mobil Corp. and Total S.A. are among the companies that have minority stakes in the facility. Much of the fuel shipped from the plant is destined for Spain and Japan. The Qatargas official claimed that their customers are "aware of what''s going on." The stoppage comes at a time when the natural gas supply to much of Europe are constrained because of a dispute between Russia and Ukraine. Qatar, a tiny but wealthy Persian Gulf state, is the world''s largest producer of liquefied natural gas. It is investing heavily to boost its production of the fuel, which is formed by cooling regular natural gas to make it easier to transport aboard ships rather than by pipeline. The country can produce nearly 31 million tons of LNG annually, according to the Qatargas official and the U.S. Energy Information Administration.