NEW YORK -- Wal-Mart is testing a same-day delivery service in select markets for customers who buy popular items online during the holiday shopping season.

The move comes as the world's largest retailer faces increasing competition from online giants like Amazon.com., which is testing same-day delivery service in 10 markets. The Bentonville, Ark.-based discounter is trying to cater to Web-savvy shoppers who are demanding more convenience.