Afternoon Movers: Sears, Canadian Natural Resource, United Continental

The S&P 500 Index was trading lower today by around 1.3%.Shares of the following three companies were subject to significant price movements:Sears (NASDAQ: SHLD): This retailer is trading more than 8% lower today. A Barron's blog post suggested that this downward spike could be related to Macy's (NYSE: M) monthly sales release.The Barron's post points out that although Macy's monthly release may have looked positive overall, it looks notably less positive without online sales. Perhaps investors are expecting Sears to issue a monthly sales release that is affected by weaker offline sales.Canadian Natural Resource (NYSE: CNQ): This oil and natural gas company's share price has declined more than 7% today. The stock may be hurting from declining oil prices, with the iPath Crude Oil ETF (NYSE: OIL) falling around 3.4% today.As of December 31st last year, oil reserves represented almost 90% of discounted projections for future revenue from Canadian Natural's total collection of reserves. What does this mean? Oil prices matter a lot to Canadian Natural Resource. Energy company Denbury Resources (NYSE: DNR) is also trading lower today.United Continental (NYSE: UAL): Today's falling oil prices also matter to United Continental, as gasoline is one of the airline's key costs. Shares of United Continental have risen around 2% today, after rising more than 1% Tuesday on an oil price decline. Shares of competing airline Delta Air Lines (NYSE: DAL) are also up today, trading around 0.3% higher.

Disclosure: At the time of this writing, I did not own shares of any companies mentioned in this post.