Other companies associated with Petrobras have also been hit. Fitch Ratings has placed Brazilian heavy construction firms on "negative watch" due to concerns the scandal will lead to contract suspensions.
"The investigation poses reputational and contract risk for companies doing business with Petrobras, including construction firms, energy offshore operators, and shipbuilders. The oil firm has said that contracts affected by inflated pricing would be revised, but not necessarily cancelled," said analysts at IHS in a note on Thursday.
In general, Brazilians are becoming less tolerant of corruption, as demonstrated by the protests in June last year, when millions took to the street to express their anger at government, Congress and political parties.
The Brazilian Senate has ruled that although the majority of the corruption uncovered occurred when Rousseff was head of the Petrobras board, there was no evidence she benefited personally.
This means that she is unlikely to be impeached, according to IHS.
"Rousseff is considered a clean politician and it is very unlikely that she was part of the corruption scheme; her surge in popularity in the early part of her first term was in large part due to the firm stance she took against ministers caught up in corruption scandals," the research provider said.
However, the scandal further undermines Rousseff after she was re-elected by a very narrow margin last month.
Read MoreBrazil's election celebration could be short-lived
Rousseff is already struggling to combat Brazil's deteriorating economy. Brazilian GDP growth fell to 2.7 percent in 2011, the year Rousseff came to power, from 7.5 percent in 2010. The government sees economic growth coming in at only 0.9 percent this year.
"At this point, markets seem very bearish (on Brazil), but we believe they are ready to become even more bearish," said Chandler.