The two new Thrift Savings Plan investment options made a lackluster debut in May, the first month in which the funds posted returns, according to the latest statistics from the Federal Retirement Thrift Investment Board. The I Fund, which invests in international stocks, lost 4.13 percent, while the S Fund, which invests in the stocks of the many small- and mid-sized companies that are not included in the S&P 500, gained 1.42 percent. The C Fund, which invests in common stocks, posted a 0.65 percent gain in May, not enough to make up for previous months' drops. The C Fund has declined by 10.55 percent over the past year. The F Fund, comprised of fixed-income bonds, gained 0.61 percent in May, while the G Fund (government securities) saw a slight increase of 0.47 percent. The monthly C, F, G, S and I Fund returns reflect net earnings on the amounts invested during the month. For an index of the performance of the C, I and S funds that is updated continuously each business day, see the "TSP Ticker" on the front page of GovExec.com. May's rates of return are listed below. The numbers in parentheses are negative.