Santos and Oil Search will have to increase their spending on the Papua New Guinea liquified natural gas (LNG) project.
Santos has a 13.5 per cent share in the project and Oil Search a 29 per cent stake.
It is operated by energy giant ExxonMobil, which holds a 33.2 per cent stake.
Exxon Mobil has upgraded its estimated capital cost for the project by about $700 million ($A682.66 million) to $15.7 billion, due to the stronger Australian dollar.
Santos said that will increase its cost by $100 million.
Oil Search said its remaining costs were approximately $750 million, which are fully covered by its current cash position of over $1 billion.
PNG LNG remains on schedule for first production in 2014.