We may also discuss certain non-GAAP financial measures in the call today. You may find a reconciliation to GAAP of these measures on our website at www.markelcorp.com in the Investor Information section under non-GAAP reconciliation or in our Quarterly Report on Form 10-Q. With that, Anne?
Anne Waleski - Chief Financial Officer
Thank you, Tom, and good morning everyone. I plan to follow the same format as in prior quarters. I will start by discussing our underwriting operations, followed by a brief discussion of our investment results, and bring the two together with a discussion of our total results.
I am pleased to say that for 2012 we are off to a good solid start. Total operating revenues grew 18% to $733 million in 2012, up from $622 million in 2011. The increase is due to a 15% increase in revenues from our insurance operations and a 43% increase in revenues from our non-insurance operations, which we refer to as Markel Ventures.
Moving into the underwriting results, first quarter 2012 gross written premiums were just under $650 million, which is an increase of 10%, compared to 2011. The increase in 2012 was due to higher gross premium volumes in each of our three operating segments. Net written premiums were approximately $580 million, up 12% to the prior year. Retentions were up slightly in 2012 at 90% compared to 88% in 2011. Earned premiums increased 14%. This increase was driven by a 23% increase in earned premium from the London Insurance Market segment.
First quarter 2011 net written and net earned premiums for the segment were reduced by approximately $9 million of reinsurance cost, associated with losses incurred during the first quarter a year ago.
Our combined ratio was 100% for 2012, compared to 112% in 2011. The combined ratio for 2012 includes $20 million or 4 points of expense related to our prospective adoption of the new GAAP accounting standards. The 2011 combined ratio included 15 points of underwriting losses related to the three catastrophe events, which occurred last year in Australia, New Zealand, and Japan. Excluding the impact of the prospective adoption of the new GAAP accounting standards in the first quarter of 2012, and the effect of the catastrophes in the first quarter of 2011, our combined ratio improved by 1 point. This improvement was due to a lower expense ratio and a lower current accident year loss ratio, partially offset by less favorable development of prior year's loss reserve. The improvement in the expense ratio is primarily due to an increase in earned premium. The improvement in the current accident year loss ratio was due to lower attritional current year losses in the Excess and Surplus line segment and to lower attritional and large energy losses in the London Insurance Market.