Walmart isn't likely to catch up to Amazon in online sales anytime soon. Last year, Amazon was responsible for 37.6% of U.S.

The analysts regularly track retail market share and found that Amazon, Walmart Inc. and Costco Wholesale Corp. accounted for about 46 percent of all incremental retail sales in the third quarter.

Walmart (NYSE: WMT) may be the largest company in the U.S. by sales, but it keeps making its top line bigger. For a while, it looked like competitor Amazon (NASDAQ: AMZN) was poised to overtake it ...