U.S. property/casualty insurers reported $26.68 billion in net income for the nine months ended Sept. 30, a 62.2% increase over the same period a year ago, according to the Insurance Services Office Inc. and the Property/Casualty Insurers Assn. of America.

Net written premiums increased 0.8% to $323.15 billion. The insurers reported a 101.2% combined ratio vs. a 100.7% ratio for the comparable period a year ago. Policyholder surplus increased 11% to $544.85 billion.

Among other results, insurers reported a 2.5% decline in net investment income earned, to $35.03 billion. However, when net realized capital gains are included, insurers reported a 49.8% increase in net investment gains, to $39.46 billion.

The data provided by Jersey City, N.J.-based ISO and the Des Plaines, Ill.-based PCI accounts for at least 96% of all business written by private U.S. property/casualty insurers.

Commenting on the net premium increase, PCI President and CEO David Sampson said in a statement that this is the first increase in nine-month written premiums since 2006, when premiums increased 5.1%. However, data suggests the increase was due to a rise in premiums for personal lines insurers, whereas “premiums for commercial line insurers remained weak,” he said.

“The deterioration in underwriting profitability as measured by the combined ratio is a particular cause for concern, because today’s low investment yields and the same long-term decline in investment leverage that helped insulate insurers from the ravages of the financial crisis and the Great Recession mean insurers now need better underwriting results just to be as profitable as they once were,” Michael R. Murray, ISO’s assistant vp for financial analysis, said in a statement.

However, assuming the economic recovery continues, “we may see some firming in insurance markets down the road as increases in demand for insurance absorb some of the excess capacity that has weighed so heavily on many insurance markets,” Mr. Murray said.

He added that while economic growth generates stronger demand for insurance, “there is a risk that inflation in claim severity will accelerate as the economy inches closer to full employment. Whether insurer’s bottom-line net income will benefit from the gathering strength in the economy remains to be seen.”