"The Proposal is considered to be opportunistic in nature and does not reflect the fair underlying asset value of the company," Santos said in a statement to the Australian stock exchange.
Santos shares jumped as much as 20 percent on news of the bid, but are still worth only half as much as a year ago.
Scepter, with offices in New York, London and Beijing, describes itself as a syndicate of ruling families, sovereign wealth funds and ultra-high net worth industrialists who have committed more than $14 billion to back large transactions.
Prince Abdul Ali Yil Kabier, a member of Brunei's ruling royal family, is a founder and director of the firm alongside financiar Rayo Withanage. Other directors include Brunei's Prince Bahar Bin Jefri Bolkiah, the United Arab Emirates' Sheikh Juma al Maktoum, former HSBC chairman John Bond and former U.S. ambassador to Qatar Patrick Theros.
Incorporated this year, the management team is made up of several former directors of Blackstone Advisory Partners in Asia.
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Santos' spokesman declined to comment on what other alternatives the company was considering. Santos received the Scepter bid on Oct. 20,
The oil and gas producer has stakes in oil and gas production in Australia, Papua New Guinea, Indonesia and Vietnam, with the jewel in its crown considered to be its 13.5 percent stake in the Papua New Guinea LNG project.
Analysts have said that stake alone could be worth more than A$5 billion, based on the value implied in a recent takeover bid by Woodside Petroleum for Oil Search, a bigger stakeholder in PNG LNG.