Dec 8 (Reuters) - Australia"s second-largest independent gas producer Santos Ltd (STO.AX) said on Wednesday it has agreed to sell a 12.5% stake in its Barossa project to a local unit of Japan"s biggest power generator JERA. JERA, one of the world"s biggest buyers of liquefied natural gas (LNG), will pay $300 million for the stake as well as for its share in the project"s development cost for this year so far, the parties said.Gas from the company"s $3.6 billion Barossa project is key to extending the life of its Darwin LNG plant as supplies coming in from the Bayu-Undan field in Timor Sea is seen drying up in the next two years. JERA already holds a 6.1% stake in Santos"s Darwin project and the deal, as per the gas producer, will bring "alignment between the Darwin LNG and Barossa JVs for the development and processing of Barossa gas through the Darwin LNG facilities."