Retail e-commerce is big and getting bigger.

In the U.S. it totaled $37.2 billion in November and December, a 15% increase over the same period in 2010, according to comScore. Annual retail e-commerce is expected to increase at a 10% compound annual growth rate through 2015, reaching $278.9 billion, according to Forrester Research.

But what about b2b e-commerce?

While retail e-commerce grabs the headlines, b2b e-commerce is a sleeping giant with massive potential, observers say. Large b2b companies, such as industrial distributor W.W. Grainger and security software company Symantec Corp., are quietly building significant e-commerce businesses.

They're doing it, in part, by following the templates of the consumer businesses. For instance, Grainger, which generates about 25% of its revenue from e-commerce, hired an e-commerce director with consumer experience. Paul Miller, VP-e-commerce, came to the company after stints at Sears Holdings Corp. and Williams-Sonoma Inc.

Alex Latham, VP-information services at Novation, a supply chain management company in the healthcare sector, said his company emulates Best Buy, Home Depot and other consumer-oriented e-commerce leaders.

“Your b2b sites are looking more and more like consumer e-commerce sites, having an improved and robust user experience,” said Chris Fletcher, research director at Gartner Inc.

David Lechler, VP-global sales at Rainmaker Systems, a cloud-based e-commerce software pro- ider that counts among its clients Hewlett-Packard Co. and Symantec, said b2b companies must figure out e-commerce because their customers are using it in their personal lives and are beginning to expect it on the job, too. “Every day, they're buying something on their iPad or buying something on their laptop,” he said.

With business buyers increasingly comfortable with e-commerce, many marketers are seeing that segment of their business soar. Beth Ely, senior VP-new channel development at Avnet Inc., said her company's e-commerce revenue increased an astonishing 270% in 2010 and another 20% last year. “We've been experiencing unprecedented growth,” she said.

Dan Stewart, director of e-commerce at Allied Electronics, said e-commerce accounted for about 40% of his company's overall business last year, up from about 9% in 2006.

Figures like that indicate that b2b e-commerce in certain sectors will be significantly more robust than in retail. Stewart said Allied expects to pass 50% in the next couple of years, while Forrester Research projects that e-commerce will account for only 11% of total retail sales by 2015.

Stewart said e-commerce is a natural extension of the sometimes impersonal way that many b2b companies already do business: That is, b2b companies typically don't sell in storefront outlets but via catalog or phone sales. “We find that for 80% of our customers, the first place they're going [to search for electronics components] is online, usually going to Google,” he said. “If we don't have a strong e-commerce presence, we have a low chance of getting those customers.”

Jim Wehmann, VP-global marketing at Digital River, an e-commerce software and consulting company, said the level of e-commerce will vary from industry to industry, as well as product to product.

Stewart said for products priced above $10,000—such as the oscilloscopes Allied offers—customers tend to want the sales process to involve a human being.

While e-commerce may never be suited for products such as commercial jets, the platforms are increasingly able to support more complex transactions and product configurations.

“I think in b2b, e-commerce is moving from less complex to more complex industries all the time,” Wehmann said.

B2b companies are embracing e-commerce for its many advantages, such as providing a 24/7 sales outlet. It can also provide a more direct relationship with customers. “You learn more about the customer and understand more about the type of business you're selling to,” Gartner's Fletcher said.

At the same time, implementing an e-commerce platform poses many hurdles. “The challenge is how to avoid channel conflict,” Fletcher said.

In addition to determining how to account for sales initiated by a reseller or distributor, b2b companies must decide how salespeople are to be compensated for e-commerce sales in their territories. “There was a lot of fear that e-commerce was going to take away jobs,” Stewart said.

In the end, however, e-commerce may relieve salespeople of secretarial tasks and order-taking, and free them to make more sales calls for new business. “Most of the sales guys I talk to don't see it as a problem at all,” Lechler said. “They see it as an opportunity.”

E-commerce platforms must also be integrated with such existing systems as ERP and CRM. Many companies say they find this process easier than integrating e-commerce with existing salespeople and channel partners. “APIs are a lot more robust now,” Wehmann said. Software-as-a-service offerings in the cloud can also make the investment in an e-commerce platform more palatable for small and midsize b2b companies.

Despite its complexity, b2b e-commerce is going to be a reality in most industries, analysts say. “Unequivocally, there's no question, you're behind the curve [if you're not working on your e-commerce strategy],” Fletcher said. “I can guarantee you, if you're not doing it, your competitors are.”