Plug Power Inc. (PLUG) - 26 million shares borrowed, 36% annualized borrowing cost:
Starting the year on a high with good 2013 earnings numbers, a $116.3m share offering and then as a casino stock labeling by Citron Research, PLUG kept short sellers interested throughout 2014.
Runners Up:
Diamond Offshore Drilling Inc. (DO) - 19 million shares borrowed, 11% annualized borrowing cost.
US Geothermal Inc. (HTM) - 1 million shares borrowed, 2% annualized borrowing cost.