Anna Patterson's last Internet search engine was so impressive that industry leader Google Inc. bought the technology in 2004 to upgrade its own system.

Anna Patterson's last Internet search engine was so impressive that industry leader Google Inc. bought the technology in 2004 to upgrade its own system.

She believes her latest invention is even more valuable — only this time it's not for sale.

Patterson instead intends to upstage Google, which she quit in 2006 to develop a more comprehensive and efficient way to scour the Internet.

The end result is Cuil, pronounced "cool." Backed by $33 million in venture capital, the search engine plans to begin processing requests for the first time today.

Cuil had kept a low profile while Patterson, her husband, Tom Costello, and two other former Google engineers — Russell Power and Louis Monier — searched for better ways to search.

Now, it's boasting time.

For starters, Cuil's search index spans 120 billion Web pages.

Patterson believes that's at least three times the size of Google's index, although there is no way to know for certain. Google stopped publicly quantifying its index's breadth nearly three years ago when the catalog spanned 8.2 billion Web pages.

Cuil won't divulge the formula it has developed to cover a wider swath of the Web with far fewer computers than Google. And Google isn't ceding the point: Spokeswoman Katie Watson said her company still believes its index is the largest.

After getting inquiries about Cuil, Google asserted on its blog Friday that it regularly scans through 1 trillion unique Web links. But Google said it doesn't index them all because they either point to similar content or would diminish the quality of its search results in some other way. The posting didn't quantify the size of Google's index.

Cuil is hoping to attract traffic by promising not to retain information about its users' search histories or surfing patterns — something that Google does, much to the consternation of privacy watchdogs.