The increase is effective immediately and backdated to the start of field development activities.
As a result, Santos will receive a cash amount reflecting its increased share of historical revenue net of past expenditure.
Under the agreement, signed in 1999 before the field was developed, each joint venture party's interest in the field would be recalculated once the field was fully developed.
This redetermination started in June 2005 and was completed in June this year. It has since been approved by the Timor Sea Designated Authority.
Bayu-Undan produces about 3.3 million tonnes of LNG per annum though it already has environmental approval to increase the Darwin plant's capacity by two thirds to 10MMtpa.