The deal follows on from a Heads of Agreement signed in September 2007 for Shell to supply the Chinese company with LNG from its stake in the Australian Gorgon project.
The HOA provided for a Sales and Purchase Agreement to be concluded before December 2008.
The latest agreement was signed in Beijing on Monday, though details such as price were not disclosed, neither was the status of previous supply agreements signed between the two companies.
Shell owns a 25 percent stake in Gorgon along with ExxonMobil, while Chevron Corp. will be the operator and holds 50 percent.
PetroChina already has an agreement with Woodside Petroleum of Australia to buy LNG from the Browse LNG project from 2013.
In April 2008, PetroChina also signed an LNG SPA with Shell and Qatargas. The LNG will be provided from the Qatargas 4 project in Qatar.
It will be shipped to PetroChinas LNG receiving terminals upon the start-up of commercial operations of these facilities. Those agreements were for 3 MTPA of LNG for 25 years.
PetroChina is building at least three LNG import terminals in Jiangsu province, Liaoning province and in Hebei.