The influence of rumors in the stock market: a case study with Petrobras

摘要: This paper analyzes the influence of rumors on price fluctuations in Stock Exchange Sao Paulo between 2007 and 2011, through a case study with Petrobras , company whose stock had largest trading volume within period. For this purpose we used historical prices cash market provided by exchange. The communications which provides clarifications regarding unofficial information disclosed press were also collected from exchange website. analysis these documents helped to create diagram represent about categorize them subject. was applied database store company’s communications. Then retrieved analyze movements. results confirm that responses its stock. At eagerness for dilute uncertainty, investors make decisions based betting credibility media disclose them, even though knowing is not always reliable. Keywords : Informal flows. Intangible capital. Price fluctuation. Rumor. market. Tacit knowledge.