NEW YORK (Bloomberg) — Aon Corp., the biggest insurance broker, and No. 2 Marsh & McLennan Cos. will expand by acquiring smaller rivals forced by the recession to find a buyer, Advisen Ltd. said.

"Consolidation will continue at a brisk pace," John Molka, an analyst with Advisen, said in a research report distributed on Friday. "Rich acquisition targets for the largest brokers remain in abundance."

Sales of property and casualty coverage in the US are contracting as job and plant cuts leave companies with less to insure. That's squeezed revenue for brokers that make commissions by matching buyers and sellers of coverage.

Aon and Marsh & McLennan, which count the world's biggest companies as clients, have reported three straight quarterly sales declines.

"Strained revenue" is also a problem for potential acquisition targets, said Molka, whose firm advises commercial insurers and brokers on industry trends. The sales decline may provide "opportunities for large brokers to snap up these targeted companies on the cheap".

Aon advanced 24 cents to $41.05 on Friday in New York Stock Exchange composite trading, giving the Chicago-based company a market value of $11.3 billion. New York-based Marsh & McLennan, worth about $13 billion, rose 51 cents, or 2.1 percent, to $24.77.

Willis Group Holdings Ltd., the third-biggest broker, fell 1 cent to $28.14. The London-based company had a market value of $4.73 billion.

Willis, led by chief executive officer Joseph Plumeri, completed the biggest industry takeover in at least nine years in October 2008 with its $1.7 billion purchase of Hilb Rogal & Hobbs Co. of Glen Allen, Virginia. Aon bought reinsurance broker Benfield Group Ltd. for about $1.4 billion the following month.

"The largest brokers are seeking out new opportunities in the middle market," Molka said. By seeking to add smaller customers, Aon and Marsh are "attempting to expand into parts of the economy where the broker behemoths have had lukewarm success".

Marsh & McLennan has said it's looking for takeovers to boost a small-client practice the firm started last year. The broker wants to be "a consolidator" of small agencies in the US, brokerage chief Daniel Glaser said in November. CEO Brian Duperreault, a Bermudian and the former CEO of Ace Ltd., brought in last year to help restore profit, has focused on the company's flagship brokerage business as he scaled back a security consulting unit.