The U.S.-listed shares of Petroleo Brasileiro S.A. /zigman2/quotes/200745132/composite PBR +1.45% , known as Petrobras, surged 2.6% on heavy volume in midday trading Thursday, after the Rio de Janeiro-based oil and gas company priced a large share offering by a selling shareholder at a slight discount. Trading volume was 64.8 million, enough to make the stock the most actively traded on major U.S. exchanges, and more than four times the full-day average of 15.9 million shares. The company disclosed in a regulatory filing that Banco Nacional de Desenvolvimento Econômico e Social (BNDES), sold 734.20 million common Petrobras shares, including 168.14 million shares in the form of American Depositary Shares (ADS), to raise about $5.2 billion. Petrobras's market capitalization is $96.8 billion. The ADS priced at $14.1646 a share, or 1.8% below Wednesday's closing price of $14.43. The stock has shed 7.2% over the past three months, while the iShares MSCI Brazil ETF /zigman2/quotes/208893627/composite EWZ +0.48% has gained 0.8% and the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.52% has tacked on 8.6%.