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:

: This retailer is trading more than 8% lower today. A Barron's

suggested that this downward spike could be related to Macy's

monthly sales

. 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.

: 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

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

is also trading lower today.

: 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

are also up today, trading around 0.3% higher.