Cleary Gottlieb Steen & Hamilton is advising Brazilian oil and gas giant Petrobras on its plan to raise nearly $75bn (£49bn) in the world's largest-ever share sale, reports The Am Law Daily.

The US firm is acting as issuer's counsel on the sale, which will finance investments in developing offshore oil fields.

Cleary capital markets partners Nicolas Grabar and Francesca Odell are leading the firm's team acting for Petrobras on the share sale. Cleary has a longstanding relationship with Petrobras, the world's fifth-largest oil producer, having in the past advised the Rio de Janeiro-based company on regulatory and corporate matters.

The state-owned company has agreed to issue $42.5bn (£27.7bn) in new stock to the Brazilian Government in order to obtain the rights to the estimated five billion barrels of oil in deepwater reserves such as the Tupi field, one of the largest offshore oil discoveries of the last 30 years.

In addition to the stock-for-oil swap, Petrobras will raise the remaining $32bn (£21bn) from stock sales to minority shareholders. That share sale alone would be the largest in the Western hemisphere for over 10 years and would raise almost 50% more than the $22bn (£14.3bn) initial public offering by the Agricultural Bank of China this July.

Offshore firm Walkers and Brazilian firm Machado Meyer Sendacz & Opice are also advising Petrobras.

Meanwhile, Shearman & Sterling capital markets partner Stuart Fleischmann and Brazilian firm Mattos Filho Veiga Filho Marrey Jr & Quiroga are advising the underwriters, which include Bank of America Merrill Lynch, Banco Bradesco BBI, Banco Santander, Citigroup Global Markets, Itau BBA and Morgan Stanley.

The Am Law Daily is a blog on law.com, Legal Week's US affiliate title.