Second agreement is expected to exceed US$17.5 billion China has intensified efforts to diversify its energy sources by striking an agreement to buy more than US$17.5 billion worth of liquefied natural gas from Australia. The announcement of the deal - the second in just over a year - came on the third day of President Hu Jintao's visit to Australia, during which he significantly strengthened ties between the two countries. Under the agreement, China National Offshore Oil Corp will buy gas from the Gorgon gas project in Western Australia for 25 years. The value of the deal has not yet been revealed but it is expected to exceed the US$17.5 billion gas deal struck between the Chinese oil firm and the owners of the North West Shelf gas project in Western Australia last year. It would be the biggest single export contract in Australian history. Under the agreement, China National's listed subsidiary, CNOOC, will buy a 'substantial' stake in the Gorgon project. It will be the third gas deal in the past 13 months between China National and foreign gas suppliers. Last year, it agreed to buy 2.6 million tonnes of gas annually for 25 years from Indonesia's Tangguh gas project and 3.4 million tonnes a year for 25 years from the North West Shelf project. China's fast economic growth saw it become a net oil importer in 1993. Its oil self-sufficiency ratio is expected to fall from 70 per cent to 50 per cent by 2020. It imports more than half its oil from the Middle East. The nation is seeking to diversify both the geographical source of its energy by buying stakes in foreign oil and gas fields, as well as the type of energy. It aims to boost the use of natural gas from 3 per cent of the nation's energy to 6 per cent by 2010. Welcoming the deal, Australia's Trade Minister, Mark Vaile, said: 'We have a golden opportunity for this country ... to resource the industrialisation of China the way we did Japan after the second world war and it is an opportunity that can't be missed.' Mr Hu also signed a trade and economic framework accord designed to set the stage for the two countries to start exploring a free-trade deal. Mr Hu said there were 'immense' opportunities for trade between China and Australia, noting that Australia's vast natural resources complemented the development needs of China's 1.3 billion people. 'Past, present or future, we see Australia as our important economic partner,' he said. Bilateral trade between the two countries has grown to US$10.4 billion from $87 million in the early 1970s. Australia is China's biggest supplier of wool and also sells large amounts of iron ore and alumina. China is Australia's third-largest source of imports, including computers, toys and textiles. Mr Hu said business deals between the two countries were increasing, with Australia having invested in 1,600 projects in China by June this year, representing a total investment of more than US$3.1 billion. China has invested in 218 projects in Australia with a contractual value of US$450 million. 'We are ready to be your long-term and stable co-operation partner, dedicated to close co-operation based on equality and mutual benefit,' Mr Hu said.