With that, I would like to now turn the call over to Mr. Jim O'Neil, Quanta's President and CEO. Jim?
James F. O'Neil
Thanks, Kip. Good morning, everyone, and welcome to Quanta Services Second Quarter 2012 Earnings Conference Call. I will start the call with an operational overview before turning it over to Derrick Jensen, Quanta's Chief Financial Officer, who will provide a detailed review of our second quarter financial results. Following Derrick's comments, we will welcome your questions.
Our second quarter results demonstrate continued solid execution by our operations and reflects strong demand for our services. Our revenues in the second quarter grew 50% compared to the second quarter of 2011, and revenues for the first 6 months of this year have increased 58% compared to the same period last year. Our GAAP diluted earnings per share of $0.31 in the second quarter increased 107% compared to the second quarter of last year.
Our second quarter results were driven by strong performance in our electric power segment due to the significant volume of electric transmission projects underway and our ability to safely execute on those projects. Quarter over quarter and sequentially, improved performance from our natural gas and pipeline segment also contributed to the strong results.
Our employee count at the end of this year's second quarter was approximately 19,300, up 30% compared to the second quarter of last year and up 10% since the end of 2011.
Our electric power segment revenues increased approximately 52% in this year's second quarter compared to the same period last year. At the end of the second quarter, 12-month backlog for the electric power segment increased 27.4%, and total backlog for this segment increased 4.1% compared to the second quarter of 2011.
In the second quarter, Quanta completed the installation of San Diego Gas and Electric Sunrise Powerlink transmission line, which was energized on June 17. This was an extremely challenging project due to the environmental sensitivities, difficult geology and geography, and an accelerated construction timeline. For environmental reasons, nearly 75% of the project's towers we're set by helicopters, resulting in more than 28,000 flight hours being logged to complete the aerial construction. The timely completion of the Sunrise Powerlink transmission line was critical due to the recent shutdown of the San Onofre nuclear plant. Because this plant supplied a significant amount of electricity to San Diego, energizing the Sunrise Powerlink line on the accelerated schedule was critical. This project, in almost every aspect, is an excellent example of Quanta's industry-leading transmission capabilities and our ability to meet our customer's expectations under challenging circumstances.
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