Borrowed shares, which are used as an indicator of the level of short selling, rose to the highest number in five years, according to Data Explorer.
The data suggests investors around the world are now increasingly betting on downward movements in the stockmarket.
Of the global stock that is available to be borrowed, 11.6% was out on loan last month, the research firm says.
The September numbers show a 9.5% increase from July, the largest rise since September 2006.
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