Option bears eye Bank of Montreal puts before results

*Volume in Bank of Montreal options jumps before earnings

*Puts outpace calls by factor of 13.23

*U.S.-listed BMO shares slip 3.1 percent

By Doris Frankel

CHICAGO, Aug 24 (Reuters) - A number of option traders on Monday took a bearish stance on Bank of Montreal (BMO.TO) (BMO.N), a day before Canada's fourth-largest bank was due to report quarterly results.

In a busy session for BMO options, volume in the stock's puts outnumbered calls by a ratio of more than 13-to-1 as investors suggested a cautious outlook.

"There are really aggressive buyers of Bank of Montreal puts going into tomorrow's earnings," said Joe Kinahan, chief derivatives strategist at thinkorswim, a division of TD Ameritrade Holding Corp. "You can see by the weakness in the stock that the prognosis is not a good one."

Results for the bank's fiscal third quarter are due before Tuesday's opening bell.

On the New York Stock Exchange, the bank's shares fell 3.1 percent to $45.57. Since hitting a 52-week low of $19.32 on Feb. 24, the stock peaked at $51.76 on Aug. 3.