Qatar Petroleum, the Gulf country’s state-run energy company, plans to raise about $3 billion from project financing next quarter to develop its Barzan natural-gas facility, two bankers familiar with the transaction said. The 16-year loans will pay an interest of between 100 basis points to 150 basis points over benchmark rates besides fees, said the bankers, who declined to be identified because the information is private. Qatar Petroleum sent out request for proposals for the loan to about 50 local and foreign banks and may complete signing documents over the next four to six weeks, the bankers said. One basis point is one hundredth of a percent. The loans will be followed by a bond offering, with a total fund-raising of $5 billion planned, the bankers said. Qatar Petroleum didn’t respond to an e-mail seeking comment. Qatar Petroleum and Exxon Mobil Corp. signed an agreement in January to develop the Barzan facility. At an estimated cost of more than $8 billion, it will be the country’s most-expensive energy project since Royal Dutch Shell announced the Pearl gas-to-liquids plant, now budgeted at about $19 billion, in 2006. Barzan’s two plants are to produce 1.4 billion cubic feet of natural gas a day for domestic needs once completed in 2015. Qatar Petroleum will own 93 percent of the project and Exxon the remainder, while Ras Laffan Liquefied Natural Gas Co, one of Qatar’s two gas liquefaction companies, will develop it.