Commercial insurance brokers based in the U.S Northeast led the nation in brokerage revenue during 2011, while those based in the West had a far smaller piece of the pie, according to a Business Insurance analysis.

To identify the leading regional brokers, Business Insurance used brokerage revenue provided by commercial insurance brokers nationwide and placed them into the regions where they are headquartered.

Brokers also were asked what proportion of their brokerage revenue was derived from middle-market business, a definition on which many differ.

Using brokerage revenue derived from U.S. clients as a gauge, New York-based Marsh & McLennan Cos. Inc. was far and away the largest commercial insurance broker headquartered in the Northeast, producing $5.07 billion in U.S.-based revenue in 2011. With 55% of that revenue coming from middle-market clients, Marsh also placed more middle-market business than any other U.S.-based broker.

Its closest competitor was National Financial Partners Corp., which produced $692.9 million in U.S.-based brokerage revenue in 2011. The New York-based brokerage declined to disclose what proportion of that business came from middle-market accounts.

With Aon P.L.C. moving its headquarters to London earlier this year, Itasca, Ill.-based Arthur J. Gallagher & Co. led the Midwest region in U.S. brokerage revenues, generating $1.69 billion in 2011, the majority of which was derived from middle-market accounts.

Closely following Gallagher was Chicago-based Wells Fargo Insurance Services USA Inc., which produced $1.63 billion in U.S. brokerage revenues in 2011, a little more than half of which came from middle-market business.

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In the South, Daytona Beach, Fla.-based Brown & Brown Inc. narrowly beat out Raleigh, N.C.-based BB&T Insurance Services Inc. Brown & Brown generated $1.11 billion in U.S. commercial brokerage revenue in 2011, while BB&T garnered $1.10 billion last year. Nearly 90% of both brokers' commercial brokerage revenue is derived from middle-market accounts.

As a group, the top five brokers based in the U.S. West trailed the other regional broker leaders. Collectively, the five largest brokers based in the West generated just less than $1 billion in U.S. commercial brokerage revenue in 2011.

But one broker emerged as a clear leader in the West: Alliant Insurance Services Inc. of Newport Beach, Calif., which produced $460.2 million in U.S. brokerage revenue in 2011.

Alliant was followed by the Leavitt Group, based in the remote and sparsely populated Southwest. Cedar City, Utah-based Leavitt Group produced $188.2 million in U.S. commercial brokerage revenue in 2011.

Neither would provide an approximation of the proportion of their business derived from middle-market accounts.

See the top five Regional mid-market broker leaders: U.S. Northeast-headquartered firms.

A ranking of the top 10 brokers in each region is available in the weekly edition of Business Insurance. To subscribe to Business Insurance, click here.