Brazilian state oil company Petrobras is set to launch the world's largest ever public share offer, which could it sell up to $US79 billion in new stock.
The value of transaction will be determined when the price of the shares is fixed later.
The BBC reports that it is worth far more than the company had anticipated, due to heavy demand.
The money will fund the development of recently-discovered oil reserves off the coast of Rio de Janeiro.
The company is issuing more than 2 billion common shares and 1.5 billion preferred shares.
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.