Petrobras’s IPO just got a little more intriguing. The Brazilian oil giant has announced that it will add another 376m shares to its offering, under an over-allocation option. That could take the IPO to a total of $79bn – three-and-a-half times the world record set by AgBank earlier this year.

The question is why. Does Petrobras think the IPO is going well or badly?

The bearish view is that demand is so low that Petrobras needs to sell the extra shares to finance its $224bn investment plan. (Thursday’s FT suggested why this may be the case: the IPO process has dissatisfied many investors, in Brazil and the US.)

As the FT reports on Thursday, many investors are unhappy about the way Petrobras and Brazil’s government, the national oil company’s controlling shareholder, have handled its forthcoming share issue, set to be the biggest ever attempted.

One measure of just how unhappy investors are is the price they have paid to rent Petrobras shares to short them in a bid to push their price down. In normal circumstances, the rate is between 1 and 2 per cent a year of their current price.

When Petrobras released the detail of its capitalisation plan on September 2, the going rate leapt to about 20 per cent. It had suddenly become hugely expensive to short Petrobras, but some investors were still eager to do so.