SYDNEY, AAP – Sydney Airport Corporation is closer to a decision on a takeover offer after letting an investor group examine its books after it raised its bid.

A group of superannuation companies has made a third bid for the airport of $8.75 per stapled security ($23.6 billion), up from a previous bid of $8.45 bid per security.

Sydney Airport said it would allow the consortium to conduct due diligence on its financials in order to make a binding offer. The due diligence is expected to take about four weeks.

The airport board said it intends to unanimously recommend security holders vote for the proposal, should a binding offer be made.

The corporation will hire a third-party expert to help assess the merits of the bid.

The Sydney Aviation Alliance consortium, which includes IFM Investors, Queensland super fund QSuper and Global Infrastructure Partners, made its first offer in July at $8.25 per stapled security.

Securities in Sydney Airport on the ASX were trading higher by five per cent to $8.40 at 1131 AEST.