MILAN- Italy's Benetton family and U.S. investment fund Blackstone have proposed a 58 billion euro ($63 billion) buyout offer for Atlantia, to take it private and stave off rival interest for the airport and motorway operator.

Highlighting the appeal of the infrastructure sector, the deal would be this year's second-biggest M&A transaction globally after Microsoft's $69 billion acquisition of Activision Blizzard.

Alessandro Benetton, chairman of the family holding company Edizione since January, said one of the aims was to preserve the integrity of Atlantia and its Italian identity, adding they had found in Blackstone a long-term co-investor and partner.

Edizione owns a third of Atlantia.

The bid heralds a new phase for Atlantia which is selling its domestic motorway unit to draw a line under a political dispute sparked by a deadly bridge collapse in 2018.

The sale, which will cut Atlantia's end-2021 debt of 38.6 billion euros, will bring 8 billion euros into its coffers. Net of debt the offer values the group at 19 billion euros.

"The gargantuan Benetton and Blackstone-led Atlantia deal redefines how investors will think about infrastructure investments due to its sheer size alone," said Wylie Fernyhough, senior private equity analyst at PitchBook.

The Benettons and Blackstone said on Thursday they would offer 23 euros per share, a premium of 24.4% to the share price on April 5, before speculation about the offer fuelled gains.

The premium rises when taking into account that investors who tender their shares will still receive a proposed dividend of 0.74 euros a share.

Blackstone, which is also part of a consortium led by Italy's state-owned lender CDP expected to complete the purchase of Atlantia's domestic motorway business next month, said it believed in the strength of the Italian economy and the future opportunities it would offer.

Shares in Atlantia, which have gained almost a fifth over the past 10 days, rose 4.4% to 22.85 euros each on Thursday.

Analysts said the bid's price appeared adequate and, with shares aligned to it, deemed a counterbid unlikely for the moment.

The Benettons last week said they were in talks with Blackstone after they rejected an approach by investment funds Global Infrastructure Partners (GIP) and Brookfield to acquire Atlantia and hand its motorway concessions to Florentino Perez's Spanish construction group ACS.

GIP, Brookfield and ACS were not immediately available for comment on Thursday.

NEW CHAPTER

The Benettons and Blackstone are set to spend up to 12.7 billion euros, financed partly with 8.2 billion euros in debt.

"The deal illustrates the depth of private markets and how attractive infrastructure assets have become in this inflationary environment," Fernyhough said.

Atlantia's delisting would open a new chapter for the company after the threat of being stripped of its motorway concession put its business at risk, while the death of 43 people in the bridge disaster tarnished its reputation.

Atlantia runs five airports and nearly 10,000 kilometres of motorway around the world.

With 33% of Atlantia already in the hands of the Benettons, the bid targets 66.9% of the group's share capital and is conditional on reaching a 90% acceptance threshold.

"There is a good chance of reaching the targeted ... threshold," Bestinver analyst Marco Opipari said.

UKRAINE CLAUSE

The offer is also subject to a clause that would allow bidders to walk away in the event of major unfavourable circumstances arising, including in relation to the Ukraine conflict.

"The material adverse change condition ... specifically carves in potential developments in Russia/Ukraine," vice president Alastair Mankin at Cowen investment bank said.

Under Italian rules, Atlantia will be allowed to give its opinion on the bid only once market regulators approve the offer's prospectus and the document is officially published.

Edizione will have 65% of the investment vehicle launching the offer for Atlantia, with the U.S. company holding the rest.

Italian banking foundation CRT, a long-time investor in Atlantia, is expected to tender its full 4.5% stake under the offer, reinvesting the proceeds into the bid's vehicle if the offer goes through.

Alessandro Benetton on Thursday said the proposed deal was open to other current investors in Atlantia, suggesting that relevant shareholders who decide to join the offer could in turn get a stake in the delisted Atlantia.

Other investors in the group include Singapore's sovereign fund GIC, with a 8.3% stake, and HSBC Holding, with a 5% stake, according to Atlantia's website.

Goldman Sachs, Mediobanca, Bank of America, JPMorgan, UBS, UniCredit are acting as financial advisers for the Benettons and Blackstone. Gatti Pavesi Bianchi Ludovici, Legance, Simpson Thacher & Bartlett LLP are legal advisers.

($1 = 0.9164 euros)

(Writing by Giulio Piovaccari; editing by Jason Neely and Jane Merriman)