South Korean stocks gained ground on Thursday though the futures and options of the main index and individual stocks matured simultaneously.

The simultaneous maturities are called a quadruple witching day when volatility tends to increase.

The benchmark Korea Composite Stock Price Index (KOSPI) gained 17.48 points, or 0.74 percent, to settle at 2,377.66. Trading volume stood at 283 million shares worth 6.3 trillion won (5.8 billion U.S. dollars).

The KOSPI, which stayed flat in early trading, picked up in late trading as institutional investors reduced their sales of stocks on the quadruple witching day.

Foreign and institutional investors sold stocks worth 204 billion won and 8 billion won respectively.

Local and foreign financial institutions usually sell, or buy, stocks on the quadruple witching day as their positions on stock futures and options, linked to shares on spot, mature.

Individual investors bolstered the KOSPI by purchasing a net 191 billion won worth of stocks. U.S. stocks picked up overnight which also helped boost market sentiment, market watchers said.

Most of large-cap shares gained ground. Market bellwether Samsung Electronics gained 1.4 percent, and the most-used search engine Naver advanced 4.9 percent. Memory chip giant SK Hynix climbed 1.5 percent, and top carmaker Hyundai Motor rose 2.2 percent.

The state-run power supplier Korea Electric Power Corp. added 0.5 percent, but the No.1 steelmaker POSCO declined 2.9 percent. Leading chemical firm LG Chem lost 0.1 percent.

South Korea's currency finished at 1,132.6 won against the greenback, down 4.1 won from the previous close.

Bond prices ended mixed. Yields on the liquid three-year treasury notes closed unchanged at 1.742 percent, but the return on the benchmark 10-year government bonds added 0.2 basis points to 2.444 percent.