After a temporary drop in the second half of March, short interest is back on the rise.
The NYSE recently reported that in the first half of April short interest rose to 13.36 billion shares from 13.23 billion on March 28, a one percent increase.
Likewise, NASDAQ also showed an increase of 1.4 percent in short interest during the same period.
According to data from FactSet, more than 58 percent of S&P 500 companies saw a spike in short interest in the first two weeks of April.
Short interest measures the total number of shares of a security that has been sold short, expressed as a percent of total tradable 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.
J.C. Penney, Gamestop and First Solar, for example, have some of the highest ratios in the S&P 500 index, with more than 30 percent of their float sold short.
Here is a look at the most heavily shorted stocks: