We had plenty of rumors running around SES NY last week that Yahoo might expand its contextual ad offerings in the manner of Google's self-serve AdSense ones. Yahoo cofounder Jerry Yang suggested in my keynote talk with him that this was pretty likely as well. Yahoo! Mulls Expansion Of Contextual Program from MediaPost today looks briefly at further fuel after Yahoo contextual ads showed up on the blog of Yahoo product manager Ken Rudman. More from Andy Baio and Olivier Duffez. How big for Yahoo? As noted in the article, Google doesn't reveal how much its own self-serve AdSense ads generate. But I suspect it's serious money. More on why is explained in my article about the Google IPO from last year: Google IPO To Happen, Files For Public Offering.Postscript: News.com has a new story on the rumors, Yahoo seeks to expand in Google territory. Also see ClickZ's Marketers React to Yahoo! AdSense Alternative.