Text Advertising market

Kontera is a PPC contextual in-text advertising provider.



PPC = Pay Per Click. Advertising revenue is only generated when the actual ad is clicked.
Contextual = Kontera's ContentLink technology analyzes the content on the page, extracts and ranks topics and keywords, and matches them to relevant advertisements.
In-text advertising = specific words within the textual content of a webpage are associated with advertising content. A word is underlined (double-underlined to differentiate it from regular hyperlinks) and when moused over (the mouse cursor is placed over the link) an in-page window appears which contains the ad. Mousing over the ad does not constitute a click.
Cons
They are contextual, much like Adsense. However while the keyword they link has something to do with the ad that is displayed, it doesn't always (in my case never) mean that the ad relates within the context of the whole article.
If you earn under $5 in a month that money does NOT roll over to the next month. They keep it.
They will only pay you out when you reach $100.
This point pulled due to it not being verified.

When an ad is clicked the target URL opens in the page that you are currently on. So that means unless the visitor uses the back button, you won't see that visitor again. That is the default (and only) setting for HubPages. But you apparently can change it in your own website.
If people are clicking on Kontera Ads, they most likely won't have the chance to click on Adsense ads. Adsense, by comparison, appears to pay more for a click than Kontera.
I've heard that you need 30 day notification to Kontera before shutting off Kontera ads on your site. Otherwise it is a TOS violation (and I assume all your unpaid revenue will be forfeit). But I am currently unable to find it listed in their Terms of Service.





Pros
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In-Text Advertising Programs
As well as Kontera the other two big competitors in the In-Text Advertising market are Vibrant and Infolinks.


from http://hubpages.com/hub/how-kontera-works