NEW YORK -- Valero Energy (VLO - Get Report) has done well along with other refiners, but bearish option traders racked up some fast money in the name on Monday. 

OptionMonster's Depth Charge system detected heavy buying in the March 59 puts early in the session, with large blocks trading for $1.31 to $1.45. Almost 9,000 contracts changed hands in the first 30 minutes, dwarfing the previous open interest of just 192 contracts. 

The oil refiner was already under pressure when the option activity hit, and shares continued to fall through the session. That drove up the value of the March 59 puts by about 50% to more than $2 by the afternoon. 

Puts locks in the price where a stock can be sold. Investors use them to hedge long positions or to speculate on a decline. Their cheap cost can also result in significant leverage if a drop occurs, as we saw Monday. 

Valero shares closed the session lower by 4.9% to $58.67, but at one point it was down almost 6%. The drop came amid selling pressure in the broader energy sector. Refiners also took a beating from weakness in European Brent crude, which is key to pricing gasoline and other products. 

Monday's overall option volume in Valero was quadruple its daily average, with puts accounting for a bearish 72% of the total. The stock had touched a seven-year high late last month. 

-- Written by David Russell of  OptionMonster 

Russell is short VLO shares.