A new study produced by Nielsen//NetRatings has found that search engines enjoy the highest user retention rates of any website category, but also had a significant audience overlap with their competitors.

This suggests that a number of web users are regularly using two or three search engines, to compare results, or perhaps according to the perceived strengths of each company’s search results.

Search engines had an average user retention rate of 71%, with Google leading the pack with retention rates of 79% for home users and 85% for work users. Yahoo Search was next on 69% for home use and 70% for work, while the same figures for MSN/Windows Live Search were 65% and 72% respectively.

Interestingly, the survey of US web users in July found that there was significant overlap in audiences for all three search engines. MSN/Windows Live Search had the highest overlap, with 84% of its unique visitors also using one or both of rivals Google and Yahoo for search. Yahoo had a 78% audience overlap, while Google’s was just 63%.

According to Ken Cassar of Nielsen//NetRatings:

“These search providers are doing a good job of bringing their visitors back month after month, which is an important sign of the health of their customer relationships and a measure with significant financial implications, given the expense of acquiring new customers.”

Both the retention and user overlap figures, as well as market share figures, indicate that Google is the top search engine for the majority of web users, though the fact that many Google users also search with other sites will encourage Yahoo and MSN, as they may be able to steal some market share from Google with enhanced features and services.