The largest share issue ever just got larger.

Brazilian state-run energy giant Petroleo Brasileiro (PBR, PETR4.BR), or Petrobras, on Friday said it has increased the amount of additional shares that will be available to investors in its ongoing capitalization program.

Petrobras has increased the amount of additional shares available if there's strong demand to 20% of the offering, up from 10% previously, the company said in a statement.

Based on Thursday's closing price for Petrobras, the company would raise as much as 128 billion Brazilian reals, or $75 billion, if the full amount of shares are sold.

"This increase in the size of the offer can be seen as a good sign for the company, it signals that there could be stronger demand by investors," said Joao Pedro Brugger, a fund manager at the Leme investment fund in Santa Catarina who oversees BRL60 million in debts and equities. "With the drop in Petrobras share prices in recent days, maybe some investors decided to get into the final part of the deal."

Petrobras is expected to set the price for the initial offering of 3.75 billion shares on Sept. 23. The additional shares would be sold at the same price, if there's enough demand.

The firm's preferred shares were flat on Friday at BRL26.35. The shares are up 1% since the beginning of September, but are down 7% from mid-August, and down 27% from the beginning of the year.

The company didn't say why it had increased the additional lot of shares.

Petrobras will use proceeds from the issuance to finance its $224 billion investment program for the next five years.

Petrobras is in the bookbuilding process, which started Sept. 3.

Bank of America Merrill Lynch, Bradesco BBI, Citibank, Itau BBA, Morgan Stanley, Banco Santander, BB Investimentos, BTG Pactual, Credit Agricole, Credit Suisse, Goldman Sachs Group Inc., HSBC, J.P. Morgan Chase & Co., Societe Generale, Espirito Santo Investment, Deutsche Bank, J. Safra and Banco Votorantim are coordinating the operation.