eBay Is Using Google In Its War Against Amazon - While Amazon Sits On The Sidelines

eBay appears to be heavily using a new type of Google ad - the "product listing ad" (PLA) - in its fight with Amazon, according to analysts at Jefferies Equity Research. But Amazon, for some reason, is sitting on the sidelines and has declined to use the new tool.

Amazon is known to be sensitive about PLAs, in part because they push down Amazon's "organic" or unpaid search results. Amazon declined comment for this story.

Until 2012, when Google launched PLAs, Amazon pages were often featured prominently in searches conducted by shoppers. Now, they're halfway down the page or worse, crammed down underneath the new PLA format, which prioritizes merchandise photos and comparative prices.

The mystery, however, is why Amazon doesn't take advantage of PLAs and buy some to advertise its own goods and merchants.

eBay is now the second biggest PLA advertiser, Jefferies estimates, and it may be buying about 6% of all PLAs. That's not a trivial amount of adspend. Companies frequently spend $100,000 or more per month on search ads, according to Marin Software. Google's revenues from PLAs likely increased 269% in 2013, Jefferies believes. Adobe, another digital marketer, says the cost-per-click of PLAs increased 70% in Q4 2013, year over year. Those are both indicators that Google is seeing an increase in the volume of advertisers running PLA campaigns.

Normally, in e-commerce, Amazon is a leader. Yet in PLAs it is nowhere to be seem. In addition to eBay, retailers like Macy's, Walmart and Etsy have piled in to PLAs. Search advertising tends to be "direct response" or "performance" based, meaning that advertisers only continue to pay for them if they work. "eBay does extensive A/B testing on all ad formats and its high usage of PLAs - after being absent in 2012 - can mean only one thing: these ads work," noted analyst Brian Pitz and his team at Jefferies Equity Research. eBay came to the format after initially being critical of it - another indicator that PLAs are a powerful new force in search advertising.

If that's true, they're probably also working for a bunch of companies owned by Amazon, too. Soap.com, Diapers.com, beautybar.com and other Amazon brands are, collectively, the sixth biggest PLA advertisers.

And that's why Amazon's absence from PLAs is all the more conspicuous. It is known to have never bought a single one.

Here's a chart of who spent the most on Google PLAs in 2013, from Jefferies:

Disclosure: Jeff Bezos is an investor in Business Insider through his personal investment company Bezos Expeditions.