A group of former Google employees is hoping to outmanouvre their old boss by developing a rival search engine they claim provides a more comprehensive guide to the web.

Cuil, which went live today, was built by Anna Patterson, a former Google employee who helped create the company's index - the enormous catalogue of web pages which its scours every time someone conducts a query.

Speaking before the launch of Cuil, which is pronounced 'cool', Ms Patterson said that one of the main reasons rival search engines such as Microsoft Windows Live and Yahoo! had struggled was because they weren't able to index as many pages as Google.

Cuil had solved that problem by compiling an index three times as large as Google's - searching for results across 120 billion web pages compared with Google's index of 40 billion pages, she said. Google does not reveal how large its index is, but in a statement today said that it welcomed competition, which "stimulates innovation and provides users with more choice."

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Rather than displaying results in a list, like Google, Cuil shows them on a page which has a more magazine-like feel. Each result has a greater amount of text alongside it, and sometimes an image as well. "You can't be an alternative search engine and smaller," Mr Patterson was quoted as saying. "You have to be alternative and bigger."

Several large and deep-pocketed rival engines have sought to reel in Google - the runaway leader in search - but none has succeeded. Last month, Google performed 82 per cent of searches in the UK last month, according to Nielsen Online, compared with 5 per cent for Yahoo!, 4 per cent for Microsoft's Windows Live Search, and 3 per cent for Ask.com.

Internet experts gave a cautious welcome to the new service today, saying the promise of a larger index of web pages was appealing but that there would likely be some teething problems as the service found its feet. Ultimately Cuil's popularity would be determined by the relevance of results, they said.

“This is the most promising thing I’ve seen in a while,” Danny Sullivan, editor of the Search Engine Land blog was quoted as saying. "Whether they are going to threaten Microsoft, much less Google - that's another story."

Based on an hour's trial, Michael Arrington, author of the technology blog TechCrunch, said that Cuil was an "excellent search engine" but that it didn't appear to have "the depth of results that Google has." He added that the results on Cuil were also less relevant, but that the engine had a 'related query' box which enabled the user to refine their query very effectively.

"Cuil does a good job of guessing what we'll want next," he said.

Drew Broomhall, search editor of Times Online, said: "It's about time people starting experiencing different ways of seeing search results. Even Google presents them in a fairly limited way."

"The big factors will be how quickly they can get fresh content such as breaking news into the search results, and how they deal with spam, where websites try to trick search engines into thinking they are more relevant than they are." The site was periodically unavailable in the UK today.

Cuil, which is based in Menlo Park, near San Francisco, has raised $33 million from venture capital investors.

As well as Ms Patterson, its founding team includes her husband, Tom Costello, who developed search technology for the computing giant IBM, and two other former Google engineers - Russell Power, who worked on the same team as Ms Patterson, and Louis Monier, who was also the chief technology officer at Alta Vista, one of the most popular pre-Google search engines.

A number of start-ups have attempted to lure users away from Google with new ways of searching, including Teoma, whose technology was incorporated into Ask.com, and Powerset, which pioneered "natural language search" - the ability to respond to questions and other sentences - and which was acquired by Microsoft earlier this month.

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