Executives at six media agencies confirmed Amazon is making huge inroads in advertising, supporting the recent eMarketer report that the tech giant has become the third largest U.S. digital advertising platform behind Google and Facebook.

One exec from a large agency said some brands find Google search ads “quaint” and want their budgets moved to Amazon because it directly correlates to sales. About 49 percent of product searches begin on Amazon, according to Survata.

Another said clients appreciate Amazon is a seamless shopping experience. Using a Google search ad to lead to a purchase may require a person to set up an account and input their credit card information with a separate website. Especially for smaller brands, there’s not really an advantage between selling direct to the consumer versus selling through Amazon.

Those budgets have to come from somewhere.

While some of the dollars are being siphoned from print, TV and programmatic display advertising, one executive at a large agency said some clients who sell products on Amazon are moving between 50 and 60 percent of their allocated Google search ad dollars specifically to Amazon. The shift amounts to hundreds of millions of dollars a year, he noted.

Another exec at a different large agency said some brands that they handle are shifting 50 percent of their Google search budgets to Amazon in certain worldwide regions. These moves also amounted to hundreds of millions of dollars a year.

A third exec, this one at a medium-size ad tech firm, said some of its clients have discussed moving large portions of their ad budgets directly from Google Search to Amazon.

For all of these advertising firms, the brands in question mostly fall in the consumer product goods category.

Chris Apostle, executive vice president and head of performance for North America at Havas Media, said his agency is seeing 20 to 30 percent of its clients shift 50 to 70 percent of their total search budgets to Amazon. Companies are realizing the more they spend with Amazon, the more they can add other bells and whistles like content or reviews that can help encourage more sales.

In general, Apostle’s clients have increased their Amazon budgets by 300 percent since last year, and he expects them to increase an additional 200 to 300 percent next year.

“Over 90 percent of searches for products that start on Amazon end with a purchase, even though that user may end up on social channels,” agreed Apostle from Havas. “The bang for your buck is where people are ultimately going to buy.”

An exec from a third large ad agency, who requested anonymity, said Amazon budgets among its clients had grown 300 to 400 percent from last year.

According IPG Mediabrand’s Reprise, the majority of the new Amazon budget is coming from a mix of sources, including programmatic display ads like banner ads, or ads bought directly from media companies — not Google specifically. Still, Amazon is growing overall, while Google budgets have remained “flat,” according to Joseph McConellouge, who leads e-retail ad buying for Reprise.

“In many cases we see see Amazon is the better performer, and by a significant margin,” he said. “If those numbers are true, we will recommend for a specific client.”