NEW YORK -- The bears racked up fast money Monday in energy companies ConocoPhillips (COP - Get Report) and Tesoro (TSO) . 

OptionMonster's Depth Charge system detected heavy put buying first in ConocoPhillips, with about 12,000 Weekly 66.50 contracts that expire this Friday trading for $1.15. A similar number of 69.50 puts were sold at the same time for $3, which indicates that a winning position was closed and rolled lower. 

Minutes later, traders purchased Tesoro's Weekly 75 puts that expire on Dec. 21 for $1.40 to $2. More than 5,800 of those traded against open interest of 2,041 contracts. 

The energy stocks were already down when the option activity began, and they continued to fall afterward. The COP puts almost doubled to about $2, and TSO's contracts soon fetched $3.60. 

Because puts lock in the right to sell a stock at a certain levels, they rise in value when shares decline. The cheap initial cost of these options can also result in significant leverage when their underlying stock prices fall. These contracts can be used either as outright bearish bets or as protective hedges on long positions. 

ConocoPhillips fell 4.16% to $65.03, and Tesoro declined 3.57% to $73.43. The entire energy sector has been crumbling since the summer, poisoned by a toxic combination of slow economic growth abroad, a strong U.S. dollar, and plunging oil prices. 

Overall option volume was more than four times average amounts in both names Monday. 

-- Written by David Russell of  OptionMonster  

Russell has no positions in COP or TSO.