Today's call may contain forward-looking statements. These statements, which we undertake no obligation to update, represent our current judgment and are subject to risks, assumptions and uncertainties. For a description of the risks that could cause our results to differ materially from those described in the forward-looking statements, please refer to the company's annual report on Form 10-K and quarterly report on Form 10-Q, which was filed with the SEC this morning.
With us today are Jeff Sprecher, Chairman and CEO; Scott Hill, Chief Financial Officer; and Chuck Vice, President and Chief Operating Officer. We'll conduct a question-and-answer session after our prepared remarks. I'll now turn the call over to Scott.
Scott A. Hill
Thanks, Kelly. Good morning, and thank you, all, for joining us on the call today. We're pleased to report our 12 consecutive quarter of double-digit earnings growth. This solid second quarter performance continues the momentum from the first quarter and reflects solid top line growth enabled by record futures volume and disciplined expense management that delivered increased operating margin.I'll begin this morning on Slide 4 of the presentation with an overview of our performance in the first half of the year. Healthy volumes across our futures and OTC energy market yielded revenue of $716 million, up 9% compared to the first half of last year. Net income attributable to ICE was $291 million, up 16% year-to-year, and operating margins expanded to 62%. Diluted earnings per share rose 18%, and operating cash flow grew 14%. Our focus on identifying and solving the challenges facing our customers gives us confidence in our ability to deliver double-digit earnings growth and strong returns on invested capital over the long term. Moving to Slide 5, I'll detail our second quarter results. Consolidated revenue rose 8% over the prior second quarter to $351 million. With expense growth of just 1% over last year's second quarter, operating income grew 13% to $215 million, and operating margin expanded 2 points to 61%.