Brought to You by . . . Anyone?

Often, most of the money a big brand spends online is for search rather than display advertising, said Kevin Kells, who handles consumer-packaged-goods advertising, both search and display, for Google. Display ads are the graphic or pictorial ads that many content sites rely on for revenue.

Search advertising allows advertisers to capture consumers' attention "at a moment of relevance," Kells said, meaning when they were looking for a product. A person searching for "fuel economy Toyota," for example, is likely to be receptive to auto ads.

"We literally buy millions of search terms," said Betsy Lazar, executive director for corporate advertising and media operations at General Motors, the nation's third-largest advertiser. " 'Chevy Detroit.' 'Chevy.' 'Fuel-efficient vehicles.' If you talk to Google, it's not that unusual."

For companies that provide Internet content, the largest source of advertising revenue is display. Such advertising accounted for 34 percent of all online ad dollars last year, according to figures from the Interactive Advertising Bureau. Search advertising is 41 percent of the total, with classified, e-mail and other categories rounding out the list.

To draw advertising revenue, online publishers and advertisers are constantly experimenting with new formats to grab attention and to better target audiences.

YouTube, which shows user-submitted videos, experimented with video ads that ran before a selected clip was shown and then opted for overlays that allow viewers to choose to watch a video ad. Facebook and MySpace, the major social networks, try to sell advertisers on the idea that their sponsored messages can spread via members. Beer companies and others post what they hope will become "viral videos" -- comic ads made to look homespun that get passed along from friend to friend.

But many online companies are looking to the big advertisers, which just haven't shown up yet, at least not in force.

The reasons are complex.

In part, many observers said, the advertising industry and its workforce are more accustomed to creating and presenting 15-second television spots or magazine ads than they are to arranging an online campaign.

Penry Price, Google's vice president of North American advertising sales, noted that while it is relatively easy to do demographic targeting in other media, it is more difficult to get precise information about online audiences for a given Web site. Consider, for example, an advertiser trying to reach young women interested in fashion.

"We know they're online, and they may be online more than they are watching TV or reading magazines, but there's no easy way to find them right now," Price said. The process of adapting to online media is "a fundamental challenge for the entire advertising industry."

In part, too, the reluctance of big brands to move online is because they have more to lose.