As the continues to trade near record highs, short interest appears to be on the rise, again.
NYSE Euronext reports short interest rose more than 1.53 percent in November to 27.84 billion shares, its largest amount in five months.
Just in the last two weeks of November, more than 43 percent of S&P 500 stocks saw an average 10 percent increase in short interest.
This year has not been kind to short sellers, which have seen the S&P jump 24 percent, or its largest gain in a decade.
But some investors believe the tide may change. Hedge fund manager Bill Fleckenstein recently told CNBC he was restarting his short fund, while hedge fund titan Jim Chanos said he's finding many more opportunities on the short side.
Short interest measures the total number of shares of a security that have been sold short, expressed as a percent of total tradeable shares.
Investors track short interest levels to gain a sense of where a stock might be headed, along with some insight into whether any positive news might force short traders to cover their positions, pushing stocks higher.
Within the S&P 500, 33 stocks or about 7 percent of the index have short interest greater than 10 percent.
About one-third of those names are part of the consumer discretionary sector. The most shorted stocks are Cliffs Natural Resources, U.S. Steel and home builder Lennar, which all have short interest greater than 20 percent.
Here is a list of S&P stocks that have the largest short interest as a percent of float and their year-to-date performance:
—By CNBC's Giovanny Moreano and Pradip Sigdyal. Follow Giovanny on Twitter: @giovannymoreano