China's biggest energy firm PetroChina is reviewing its multi-billion-dollar push to produce liquefied natural gas (LNG) to fuel trucks and ships in place of diesel, shutting two major gas liquefaction plants, sources said. Seen just a year ago as a fast-growing profit engine, PetroChina unit Kunlun Energy Co Ltd is now reconsidering its investment in the niche business after being wrongfooted by rising costs and China's slower economic growth, two sources with direct knowledge of the situation said. China, which controls energy prices to curb inflation, has announced hikes in wholesale natural gas prices totalling 33 percent since mid-2013 as part of its long-term market reforms.