Despite higher catastrophe costs, Liberty Mutual Holding Co. Inc. and its subsidiaries reported net income of $276 million for the three months ended March 31, 2015, an increase of $11 million or 4.2 percent over the same period in 2014.

Underwriting results were strong with a combined ratio of 97.1 (an improvement of 2.4 points over last year’s first quarter) and net written premium was $9.399 billion, an increase of 7.0 percent, the company said.

Revenues for the three months were $9.680 billion, an increase of $18 million or 0.2 percent over the same period in 2014.

Net operating income was $426 million, a decrease of $126 million or 22.8 percent from last year’s first quarter.

Catastrophe losses for the three months were $496 million, an increase of $9 million or 1.8 percent over the same period in 2014. The covered events included severe winter storms in the U.S., U.K. and Ireland floods.

David H. Long, chairman and CEO of Liberty Mutual Insurance, said that in addition to feeling the effects of severe winter weather, the insurer also battled market pressures in the energy sector.