East Timor (Timor-Leste) has reached an agreement with US energy firm ConocoPhillips to acquire 30% stake in the Greater Sunrise oil and gas fields, off the country’s southern coast, in a transaction valued at $350m.

A delegation headed by former East Timor president and Prime Minister Xanana Gusmao and ConocoPhillips Australia president Chris Wilson signed a final agreement in Bali.

The Sunrise and Troubadour gas fields, collectively known as Greater Sunrise, were discovered in 1974, and are located in the waters between Timor-Leste and Australia. Other owners of the Greater Sunrise oil and gas fields include Japan-based Osaka Gas.

The Greater Sunrise oil and gas fields are estimated to hold about 5.13 trillion cubic feet of gas and 226 million barrels of condensates.

The value of gas and crude oil reserves has been estimated at approximately $40bn, according to the project operator Woodside Petroleum.

“While we are aware of unofficial reports, the Sunrise Joint Venture has not been approached formally by Timor-Leste or ConocoPhillips on this matter.”

In an email to Reuters, Woodside Petroleum said: “While we are aware of unofficial reports, the Sunrise Joint Venture has not been approached formally by Timor-Leste or ConocoPhillips on this matter.”

A maritime boundary agreement was signed in March under which East Timor will secure 70% of the royalty revenues from the fields if the gas is piped to its shores or 80% if piped to Australia.

The maritime boundary pact is expected to be ratified by the end of 2018 by the Parliament of Australia.

East Timor is looking to bring gas to its shores to develop oil and gas-based industries, including petrochemicals manufacturing.