One of the biggest foreign takeovers in Australian history will force regulators and politicians to weigh who controls critical energy infrastructure against the need to address a looming domestic gas shortfall.

Santos said XRG, an investment arm of the Abu Dhabi National Oil Company, had made an indicative cash offer of $5.76 a share, valuing the Adelaide-based company at $18.7bn. It represents a 28 per cent premium to Santos’s closing share price last week.

But the offer for the ASX’s second-largest oil and gas producer has been met with a lukewarm reception from investors, who say the price could be higher.