Dongkuk Steel Mill Co., South Korea's No. 3 steelmaker, said Monday that it swung to the black in the second quarter from a year earlier largely thanks to increased prices and output. Net profit reached 108 billion won (US$101 million) in the April-June period, compared with a loss of 11 billion won a year earlier, the company said in a regulatory filing. Sales surged 21 percent to 1.58 trillion won over the cited period, and operating income more than tripled to 143 billion won, it said. Shares of Dongkuk Steel closed at 30,000 won on the Seoul bourse, up 9.89 percent from the previous session's close. The second-quarter business results were released after the market closed. The steelmaker said increased prices of steel goods such as ship plates helped boost the second-quarter earnings. Also, increased demand for high-priced products contributed to the better-than-expected bottom line, it said. In May last year, the steelmaker started operating its third plant in the southwestern coastal city of Dangjin, about 120 kilometers southwest of Seoul, which has an annual production capacity of 1.5 million tons of steel plates for ships.