Cuil, pronounced “cool,” is only the latest in a long string of start-up companies that have been founded and financed with the goal of competing with Google, as well as Yahoo and Microsoft. (In June, Google accounted for 61.5 percent of search queries in the United States, while Yahoo held 20.9 percent and Microsoft had 9.2 percent, according to comScore.) Some of the most prominent include Powerset, which Microsoft recently bought, and Wikia, which was founded by Jimmy Wales, one of the creators of Wikipedia. So far, none have managed to make a dent in the search market.

Image The makers of the Cuil search engine say it should provide better results and show them in a more attractive manner.

But some analysts say Cuil has potential, in part because of the pedigree of its founders.

“This is the most promising thing I’ve seen in a while,” said Danny Sullivan, who has followed the online search business for more than a decade and is the editor of Search Engine Land. “Whether they are going to threaten Microsoft, much less Google, that’s another story.”

Mr. Costello, a former researcher at Stanford, said that with 120 billion Web pages, Cuil’s search index is larger than any other. The company uses a form of data mining to group Web pages by content, which makes the search engine more efficient, he said. Instead of showing results as short snippets of text and images with links, it displays longer entries and uses more pictures. It also provides tools to help users further refine their queries.

Google would not comment on Cuil and would not disclose the size of its own index. But in an e-mail statement, Google said that it maintained “the largest collection of documents searchable on the Web” and welcomed competition.