The Brazilian state oil company, Petrobras, has unveiled plans to sell up to $64.5bn (£41.7bn) of new stock, in one of the world's largest public share offerings.
The transaction could be expanded to as much as $74.7bn if there were heavy demand, the company said.
The money will fund the development of recently-discovered oil reserves off the coast of Rio de Janeiro.
Shares in Petrobras rose 4% in late afternoon trade in Sao Paulo.
The company said it would issue 2.17bn common shares and 1.58bn preferred shares.
The price of the new shares will be announced on 23 September.
A public share offer had been expected earlier this year but was delayed while a deal was sorted out over how many shares the Brazilian government would receive in return for giving Petrobras access to up to 5bn barrels of oil.
Some investors have questioned the price of $8.51 (£5.52) per barrel eventually agreed in the oil-for-shares swap, believing that $5 to $6 would have been fair.