The big Adelaide-based oil and gas producer Santos has received a $13.5 billion takeover offer from the US-owned, private-equity backed Harbour Energy.

The $6.50 bid represents a 30 per cent premium above Santos’ last closing price.

The highly conditional bid is made up of a $6.13 per share cash and a 37 cent per share dividend.

Harbour has made three offers for Santos since August last year, the last pitched at $6.37 last month.

In a statement to the ASX, Santos said: “based on the indicative offer price of $6.50 per share, it is in the interests of shareholders to engage further with Harbour.”

However, the board advised shareholders to take no further action in relation until it had time to assess the bid.

Santos is Australia’s second-largest independent oil and gas producer and one of the east-coast’s biggest domestic gas suppliers.

It was founded in 1954, concentrating its early exploration in the Cooper Basin as South Australia Northern Territory Oil search.

-ABC