The 100 largest business-to-business advertisers last year spent an estimated $4.9 billion on U.S. b-to-b ads, up 3.4% over 2012, according to Ad Age DataCenter's analysis of measured-media spending data from Kantar Media.

Estimated 2013 U.S. measured-media spending for the universe of b-to-b advertisers -- the BtoB 100 and everyone else -- declined 0.5% to $10.2 billion. The top 100 accounted for nearly half of that spending.

B-to-b spending for advertisers smaller than the BtoB 100 fell 3.8% last year.

Figures include estimated b-to-b ad spending across TV, internet (display ads only), magazines (including business publications), newspapers, radio and outdoor.

The divergence in spending of big vs. small b-to-b marketers tracks with overall (business-to-consumer and b-to-b) ad spending. Overall measured-media spending last year rose 3.2% for Ad Age's 100 Leading National Advertisers and 3.3% for midsize advertisers (Nos. 101-1,000) but dropped 6.6% for small spenders (Nos. 1,000-plus), according to data from WPP's Kantar Media. Total U.S. measured-media spending last year grew by 0.9%.

The fastest-growing b-to-b measured medium last year was internet display advertising, where spending for the BtoB 100 surged 25.3% over 2012. The BtoB 100's spending on internet display ads last year passed spending in magazines.

The top 100 boosted TV ad spending by 3.0%. Spending on outdoor ads among the BtoB 100 increased 2.4%.

Ad spending by the top 100 declined in all other measured-media categories, including radio (down 13.7%), newspapers (down 9.4%) and magazines (b-to-b and consumer titles, down a combined 0.3%).
The No. 1 U.S. b-to-b advertiser last year was Microsoft Corp., which spent an estimated $290.6 million on b-to-b ads, up 34.6% over 2012.

"The fact is, we are a clear market leader in some businesses, and when you are, you drive a campaign in a certain way, but in some ways we're challengers -- as with search, phone and in the tablet [market]," said Chris Capossela, exec VP-CMO at Microsoft, in an interview with Advertising Age earlier this year. "As a marketer, we're in so many businesses, we often have to see ourselves as a leader and challenger."

Microsoft went head-to-head with Google last year with an integrated campaign, "Scroogled," that bashed the internet-media company on everything from using "invasive" ads in Gmail to sharing data with app developers. The campaign included TV and online.

Microsoft also took aim at Apple with a TV ad called "Windows 8: Less Talking, More Doing," which poked fun at Apple's virtual assistant Siri.

Apple was the nation's No. 2 b-to-b advertiser last year, spending an estimated $218.1 million on b-to-b ads, up 39.0%. The bulk of that spending was on TV.

In one of its most memorable TV ads of 2013, called "Pencil," Apple used beautiful imagery of modern office buildings, laboratories and classrooms superimposed behind a table holding a pencil, with a voiceover describing how such a "simple tool" could create new ways to work and share. At the end of the spot, an iPad Air is lifted from behind the pencil.

The No. 3 U.S. b-to-b advertiser last year was AT&T, which spent an estimated $201.3 million on b-to-b ads, up 6.6%.

The remaining top 10 b-to-b advertisers last year were, in order of spending, Verizon Communications, Google, Samsung Electronics Co., IBM Corp., Berkshire Hathaway, Intuit and Office Depot.