Share issue was to explore the offshore oil fields, which are so big they could make Brazil a major exporter.
Brazil's state-run Petrobras became the world's third-biggest oil firm by market capitalization on Sept. 27 as it completed a record share issue expected to bring in around $70 billion.
The offering has made Petrobras the third largest oil company in the world after ExxonMobil and PetroChina.
Brokers, though, said a long-term "uncertainty, a negative pressure" lingered over the shares because of doubts over investors' returns.
The government's increase in its stake in Petrobras, from 40% to 48%, also generated concerns.
"The degree of government intervention in decisions during the whole (capitalization) process was too high for a publicly listed company," said Miriam Leitao, an economic columnist for the newspaper O Globo. She noted that Petrobras had lost a quarter of its value over this year because of that preoccupation.
"Small investors are in the hands of the government," Fabio Knczuk, an economics professor at the University of Sao Paulo, said.
Petrobras is to use the proceeds from the share sale to explore the offshore oil fields, which are so big they could make Brazil a major exporter. The company wants to boost capital expenditure over the next five years to $224 billion to exploit the fresh reserves. Petrobras estimates the so-called subsalt fields could more than triple its existing proven oil reserves of 14 billion barrels.
Copyright Agence France-Presse, 2010