Backed by strong underwriting results, net income for the U.S. property/casualty insurance sector rose 40.9% to $14.4 billion in first-quarter 2013 compared with $10.2 billion in first-quarter of 2012, the Insurance Services Office Inc. and the Property Casualty Insurers Association of America said Monday.

First-quarter 2013 net written premiums increased 4.1% to $117.1 billion. Reflecting premium growth, increased reserve releases and a decline in weather-related catastrophe losses, the property/casualty industry's $4.6 billion gain in net premiums written marks its first profitable underwriting quarter since the fourth quarter of 2009, according to the report.

Indeed, the quarter is one of just 17 profitable underwriting quarters since the study began in 1986, Jersey City, N.J.-based ISO and Chicago-based PCI said.

“Underwriting results improved for all major sectors of the industry, with results for commercial insurers improving far more than those of other insurers,” Robert Gordon, PCI's senior vice president of policy development and research, said in a statement. “Excluding mortgage and financial guarantee insurers, commercial lines insurers' combined ratio dropped 6.2 percentage points to 91.1% in first-quarter 2013 as balanced insurers' combined ratio receded 0.7 percentage points to 97.5% and personal lines insurers' combined ratio fell 0.9 percentage points to 96.2%.”

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The positive underwriting results are important given ongoing low interest rates, said Michael R. Murray, assistant vice president of financial analysis at ISO.

“The net gain on underwriting for the first quarter of this year is especially welcome given the toll that long-term declines in interest rates and investment leverage have taken on insurers' ability to use investment earnings to balance underwriting losses,” Mr. Murray said in the statement. Since 1962, the yield on 10-year Treasury notes fell from a record high 15.8% on Sept. 30, 1981, to a record low 1.4% on July 25, 2012 and rose only to 2.4% as of June 20 this year, he said.