One of Google's emerging rivals for online ad dollars is also its biggest search-ad buyer.
Amazon spent $157.7 million on Google U.S. search ads in 2013, by far the most by any company, according to Ad Age DataCenter's first ranking based on data from AdGooroo, a Kantar Media company focused on search marketing.
It may raise a few eyebrows to see Amazon atop the list of Google's biggest spenders. Over the past few years Amazon has ramped up its business of selling search and display ads on its own and others' sites, putting it in direct competition with Google's ad business. Last year Amazon generated $750 million from worldwide advertising revenue and is expected to pull in more than $1 billion this year, according to estimates from digital data firm eMarketer.
Google's top 25 U.S. search-ad buyers alone spent $1.34 billion last year.
Spokeswomen for Google and Amazon declined to comment for this story.
AdGooroo CEO Rich Stokes notes that while Amazon is a growing online ad player, at its core the company is a retail giant, and retailers embrace search advertising to push sales.
Amazon is a big spender on search in general. In July 2014, the company spent nearly $19.5 million on Google search ads and $1.2 million on Microsoft Corp.'s Bing search ads, according to Mr. Stokes.
"I'm not really seeing any surprises here," Mr. Stokes said.
If anything, the list's biggest stunner may be its relatively low number of retailers.
Walmart Stores and Sears Holdings Corp. (parent of Sears and Kmart) cracked the top 10, and four other retailers made the list of the 25 biggest spenders. However, there's good reason to have expected more stores to make the ranking, considering that search is the dominant digital-ad format for direct-response advertisers like retail brands. Retailers are expected to spend more than double what any other brand category will pay for digital direct-response ads this year, according to eMarketer.
So where is the spending going? Retailers appear to be redirecting their Google search dollars to ads on product-search service Google Shopping. (Such ads until recently were called Product Listing Ads, or PLA.) "Retailers are underrepresented [in the top-25 search-spenders ranking], but that makes sense because of PLA," Mr. Stokes said, noting the AdGooroo data don't include spending on that retail-specific ad unit.
The search-spending list also appears to be short on brand advertisers. In recent years, Google has tried to attract more brand budgets to spur ad revenue as savvy direct-response advertisers have largely fixed their spend levels in place. YouTube and display ads have been at the center of Google's brand push, but last year the company also tested big banner-like images appended to search ads. Google canceled that test months later.
Despite Google's and other companies' efforts, search and digital advertising remain the domain of direct-response advertisers. Direct-response advertising accounted for 58.4% of U.S. digital-ad spending in 2013, according to eMarketer estimates, and that's expected to tick up this year to 59.1%.
Marketers in the four top-spending digital advertiser categories -- retail, financial services, auto and telecom -- spend the majority of their U.S. digital-ad budgets on direct-response ads, eMarketer found. Seventeen of the 25 companies on the AdGooroo list are brands or -- in cases such as Berkshire Hathaway, parent of Geico -- own brands that fall into one of those four groups.
The ranking is based on AdGooroo data for desktop search ads on Google's properties. Figures do not include mobile search ads or search ads shown on third-party properties that use Google as their sites' search engine.
The ranking groups various brands by parent company. For example, Amazon's spending figures include the e-commerce site's Google search spending as well as spending by other Amazon-owned companies like Zappos and Diapers.com.