NEW YORK ( TheStreet)-- Citigroup's ( C) big rally in the first half of March didn't keep short-sellers from stepping up their bets against the stock. Citigroup short interest in the first half of March rose to 552 million shares from 482 million during the previous two-week period. The rise came despite the fact that Citigroup shares soared nearly 17% during the first 10 trading days of March, and marks at least the eighth straight time Citigroup saw a rise in short interest since I began tracking the data. Short-sellers borrow shares in the hope of buying them at a lower price in the future and pocketing the difference. The most obvious explanation for the continued rise in short interest is the continued overhang of the government's 27% stake in Citigroup. On Dec 17, the Treasury postponed a share sale after it became apparent the offering price would be below the $3.25 the government originally paid for its Citigroup shares. That sparked a massive selloff in Citigroup shares, which opened nearly 10% lower on the news. Citigroup is by far the most heavily shorted ticker on the New York Stock Exchange, though that is to be expected given its roughly $4.25 stock price and massive float, which make it the most heavily traded name virtually every day. During the first half of March, it saw average daily volumes of nearly 638 million shares, higher than the short interest. By contrast, Synovus Financial ( SNV), No. 22 on the NYSE list of most heavily shorted tickers, saw 55 million in short interest on average daily volumes of 17 million. Still, the heavy short interest in Citigroup makes it increasingly unique among its large bank brethren. Bank of America ( BAC), short interest, which had been rising along with Citigroup for several weeks, saw a reversal of that trend in the second half of February. That reversal continued in March, as Bank of America short interest fell to 105 million shares from 122 million during the previous reporting period. (The NYSE releases short interest data roughly every two weeks.)
Another company that saw a notable increase in short interest in the first half of March was Sara Lee ( SLE), in which short interest jumped to 45 million shares from 16 million during the previous period. Frontier Communications ( FTR) and CBS ( CBS) also saw sizeable jumps. Warren Buffett, meanwhile, caught some relief from short-sellers. Short interest in Berkshire Hathaway ( BRK.B)"B" shares fell to 35 million shares from 58 million, following a big jump at the end of February. -- Written by Dan Freed in New York.