NEW YORK - Southwest Airlines Co (LUV.N) topped the list of the 50 best U.S. places to work, based upon employee opinions, according to research released on Wednesday.

General Mills (GIS.N), which topped the list in 2008, slipped to second place although Chief Executive Ken Powell won the highest approval rating among the top company executives, said the analysis by Glassdoor.com, a jobs website.

Glassdoor.com collected and compiled reviews from U.S.-based company employees throughout 2009.

Third place went to Slalom Consulting, followed by Bain & Co and McKinsey & Co.

What the top companies had in common was providing opportunities for employees to grow, said Robert Hohman, co-founder and chief executive of Glassdoor.com.

What I saw again and again in the reviews is employees referred to their ability to grow in their jobs. In an economic downturn like this, employees feel good if they're growing as individuals and they're becoming more marketable, he said.

Conversely at some of the companies that haven't done so well, you see things like employees feeling like they still have a job but with no opportunity, he said.

Listed as the worst place to work was Gibson Guitar GIBSN.UL, followed by United Airlines (UAUA.O), Spherion (SFN.N), AutoZone (AZO.N) and Rain Bird.

In many cases they mishandled the instability so there was a constant threat of layoffs and unclear vision of where the company was going, Hohman said.

This marked the first time Southwest was listed among the best places to work. In 2008, it did not receive enough reviews to be eligible, a spokeswoman said. Slalom also was new to the list this year.

Among the companies whose rankings shifted dramatically, FedEx (FDX.N) moved up to 21st from 49th place in 2008. Employees felt FedEx handled downsizing well, Hohman said.

Whole Foods Market Inc (WFMI.O) fell to 48th from sixth place last year. While the company remained a good place to work, employees expressed distaste for Chief Executive John Mackey, who in 2007 was found posting messages on a Yahoo! chat forum under an alias, criticizing Wild Oats Markets Inc, a rival that Whole Foods was seeking to acquire.

The lists were based on responses from more than 100,000 employees who answered surveys between Dec. 1, 2008 and Dec. 1, 2009 on such issues as work/life balance, career opportunities, compensation, benefits and employee morale. There were 11,000 companies considered. No margin of error was provided.

Employees also were asked whether they approved or disapproved of the job a CEO was doing, Glassdoor.com said.

Glassdoor.com provides reviews, salary information and interview experiences on more than 37,000 companies globally, submitted anonymously by employees, former employees and job applicants. (Editing by Eric Walsh)

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