But the site seemed unable to handle some softball, straight-forward queries. For example, a search for "barack obama" returned on the first page of results mostly links to different pages of Obama's official site, hardly useful if one is looking for a variety of sites on the presidential candidate. A search for "St. Louis, MO" initially returned zero results.

Among others, search engine expert Danny Sullivan criticized Cuil for focusing on the size of its index -- a practice that fell into disfavor years ago, as engines focused on the quality of results -- and questioned the basic validity of the claim.

"Yes, size matters. You want to have a comprehensive collection of documents from across the web. But having a lot of documents doesn't mean you are most relevant," Sullivan wrote on his Search Engine Land blog.

Sullivan also pointed out that Google hasn't publicly stated the size of its Web index in years, and that even if Cuil's is indeed three times as big, Google could quickly match that by simply becoming a bit less selective. Last Friday, Google, likely anticipating Cuil's launch on Monday, said its crawlers today "see" more than 1 trillion URLs on the Web.

Google declined to comment about Cuil's claim and also declined to say how many links are in its Web index.

Sullivan and other search market observers said they were underwhelmed by the quality of Cuil's results.

"With the huge caveat that nine queries are far from letting anyone conclude anything, I still didn't come away with a sense that Cuil has Google-beating relevancy. Instead, it has some flaws though is better than many start-up search engines appear out of the box," Sullivan wrote in another post Monday.

"I played with the site a fair bit when it turned on this morning. So far it doesn’t do much for me," wrote Saul Hansell of The New York Times in a blog post titled "Cuil’s New Search Engine: Cheaper Than Google, but Not Better."

Cuil, which is pronounced "cool," got a resounding thumbs-down from The Wall Street Journal's John Paczkowski in an AllThingsD post titled Totally UnCuil.

"If your mission is to beat Google in the search market, it’s probably wise to give your upstart search engine a name that people know how to pronounce. It’s also wise to make sure that it appears in the first page of search results for its own name. Cuil, the upstart search engine that debuted today with aspirations of unseating Google, has apparently done neither," he wrote.