Marriott.com has become the eighth-largest retail website in the world, based on revenue, behind sites such as Amazon.com and Expedia.com and ahead of computer-makers Dell Inc. and Hewlett-Packard Co. Through Marriott.com, the Bethesda, Maryland-based lodging company sold $3.7 billion worth of rooms in 2006, more than doubling revenue from the site in 2004. For the first half of 2007, Web sales for Marriott hotels, which range from luxury Ritz-Carltons to lower-priced Fairfield Inns, were up almost 25 percent.