Fewer U.S. car owners than ever are looking to switch auto insurance carriers, even as the companies boost spending to attract new business, market research company J.D. Power and Associates found in a new survey released on Monday.

One in four customers shopped for a new insurer in 2011, down from one in three in 2010, J.D. Power said. The study of more than 16,000 people was conducted in January and February.

The survey did not indicate why people shopped around.

Among those who did shop around, 43 percent switched carriers in 2011, an increase from 40 percent the previous year. Roughly one in three of those who shopped around said they had obtained quotes online, and a similar percentage said they would prefer to purchase insurance online.

The survey did not state the percentage of car owners - among those who switched carriers - who actually did end up buying insurance online.

Auto insurance is one of the most competitive segments of the insurance industry; the 10 largest auto insurers in the United States have less than 70 percent market share, according to the Insurance Information Institute. J.D. Power cited a Dowling and Partners study that said advertising spending by auto insurers rose 12 percent last year.

Some of the most prominent advertisers had some of the worst scores in the study, which looked at customer satisfaction with the shopping experience.

Allstate and Progressive -- the former known for its "Mayhem" ads and the later for sales clerk "Flo" -- both ranked in the bottom five of the 24 insurers covered. Topping the customer satisfaction list was Hartford Financial, followed closely by Liberty Mutual.

Allstate and Progressive are the second- and fourth-largest U.S. auto insurers by premiums written, according to the institute. Liberty Mutual ranks sixth and Hartford is not in the top 10.

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