The commercial insurance market saw some rate increases over the past year, which provided a slight tail wind for brokerages, but the brokers that saw the largest revenue increases mostly relied on acquisitions to drive their growth.

Among the world’s largest insurance brokers, USI Insurance Services L.L.C. reported the biggest revenue increase with a 58.7% jump, largely due to its purchase of Wells Fargo Insurance Services USA Inc.

London-based Jardine Lloyd Thompson Group P.L.C., which benefited from a stronger British pound, saw brokerage revenue jump 20.3%; and Hub International Ltd., which bought more than 50 smaller brokers in 2017, reported a 13.5% increase.

Among the Top 10, only Aon P.L.C. reported lower revenue — down 14.1% — which was due to the sale of its benefits outsourcing business to Blackstone Group L.P. last year. Despite the big divestiture, Aon, too, was on the acquisition trail, sealing more than 20 deals in 2017.

More examples of acquisition-fueled growth could be seen among private equity-owned brokers in the ranking of the largest brokers of U.S. business. Alliant Insurance Services Inc., NFP Corp., AssuredPartners Inc., Acrisure L.L.C., BroadStreet Partners Inc. and EPIC Insurance Brokers & Consultants — ranked 10 through 15 on the Top 100 ranking, respectively — all reported significant growth as they rolled up smaller rivals. Several firms that were in the Top 100 last year were among those bought or are in the process of being bought by larger rivals, including Crystal & Company, Regions Insurance Group Inc., Frenkel & Co. and Key Insurance & Benefits Services Inc.

The strong demand for insurance brokers, particularly from private equity buyers, appears to be growing as their price continues to rise.

“There’s a lot of deal flow, and the valuations have gone up a little bit,” said Timothy J. Cunningham, managing director at Optis Partners L.L.C., a Chicago-based mergers and acquisitions advisory firm and consultancy.

“What’s driving it is that there’s more players, so there’s more competition for the good properties,” he said.

“We’re definitely seeing greater competition for good acquisition properties, which is basically raising the multiple that companies need to pay to win the property,” said Mark Dwelle, director of insurance equity research at RBC Capital Markets L.L.C. in Richmond, Virginia.

And more private equity money is flowing into the brokerage sector, creating start-ups, said Phil Trem, executive vice president at brokerage consulting firm Marsh, Berry & Co. Inc. in Woodmere, Ohio.

“There are still 24-25 viable private equity-backed brokers in the marketplace, and that number continues to grow. We could be into the high 20s by the end of the year,” he said.

The average valuation for insurance brokerage firms sold in 2018 is just shy of eight times earnings before interest, taxes and amortization, Mr. Trem said. Such high valuations are unlikely to increase much more, but there is little sign of prices falling, he said.

Brokers have also seen some increases in commissions due to higher rates in some lines after the record catastrophe losses in 2017, but rates have changed little on average across all commercial lines.

“The effect on rate of 2017 storms has overall been minimal to this point,” said Marc Cohen, president and CEO of Hub International Ltd. in Chicago.

Policyholders with catastrophe exposures have seen some increases, but the storms had little effect on pricing for policyholders in most regions, he said.

Ron Lockton, president and CEO of Kansas City, Missouri-based Lockton Cos. L.L.C., said the market is “fairly steady” and the “much-talked-about hardening of the property market that we heard about several months back sort of failed to materialize.”

“The overall direction of the market is still unclear, but what we are seeing today is the market is varying by line of coverage,” with rates ranging from single-digit decreases on certain lines of coverage to mid-single-digit increases for “more challenging” coverage lines, he said.

“If you’re up less than 1% and down less than 1%, you’re in a flat market,” said J. Patrick Gallagher Jr., chairman, president and CEO of Arthur J. Gallagher & Co. “I don’t see any signs of it changing.” But increased economic activity is driving more insurance purchases.

“There’s rate in some particular lines, but in aggregate, if you look at what we’ve seen to date, exposure growth has had more impact than rate,” said Michael J. O’Connor, co-president of Aon P.L.C.

And general market forces are having less effect on insurance rates than in the past, he said. “The world is evolving to the point where — driven by data and analytics — it is a specific risk-by-risk evaluation,” Mr. O’Connor said.

Data and the technology used to evaluate it are driving more changes in the brokerage sector, said Elyse Greenspan, director of equity research for property/casualty insurance at Wells Fargo Securities L.L.C. in New York.

“There have been investments in the data side in being able to place the business faster,” she said. “That’s a reason some of these brokers have been able to see margin improvement. You continue to see more efficiency at the brokers.”

Technology will continue to drive more change in the sector, said J. Powell Brown, president and CEO of Daytona Beach, Florida-based Brown & Brown Inc. “Insurtech has the ability to automate highly repeatable tasks in our industry, and over time machine learning will add value to the insurance equation on the underwriting side and, potentially, on the broker side.”

But the disruptive power of technology has not been fully felt by insurance brokers because the insurtech sector is still small, said J. Paul Newsome, managing director for equity research at Sandler O’Neill & Partners in Chicago.

“A lot of these insurtech opportunities are really interesting and have a great chance of changing the industry, but it’s a ways off,” he said.

Judy Greenwald and Mark A. Hofmann contributed to this report.