Online advertising expense as a percentage of gross profit is 10 bps lower than prior year. We continue to see lower year-over-year ROIs, business mix shift into our international brands and to pay channels for certain of our brands. The inclusion of KAYAK provides an offsetting favorable impact on our online efficiency until we anniversary the acquisition because KAYAK spent less relatively on online advertising as a percentage of gross profit and spending by our other brands for ad placements on KAYAK is eliminated from our consolidated results.
Other OpEx besides advertising levered compared to prior year mainly because Q3 2012 included the $13 million one-time payroll tax charge in the Netherlands and $4.8 million charge related to an unfavorable hotel margin tax judgment in Washington D.C. As I will discuss in a moment when we get to Q4 guidance, we believe it is likely that the Dutch government will enact a similar payroll tax levy in Q4 2013, which will negatively impact year-over-year margins for that quarter.
Our operating margin performance was better than the 250 bps of operating deleverage assumed in our guidance forecast due to gross profit over-performance, better than assumed ad efficiency, and lower than forecasted other operating expenses.
Adjusted EBITDA for Q3 amounted to $1.11 billion, which exceeded the top end of our guidance range of $1.06 billion, and represents 43% growth versus prior year.
Non-GAAP net income grew by 44% and non-GAAP EPS grew by 40%, reflecting the impact of a higher fully diluted share count.
In terms of cash flow, we generated approximately $970 million of cash from operations during the third quarter of 2013, which is about 44% higher than last year. We spent about $20 million on CapEx and repurchased $460 million of our common stock in Q3.
Since the KAYAK acquisition, we have in total spent $805 million to purchase about 916,000 shares of our common stock at an average price of $878 per share, to partly offset dilution from the shares issued to close the KAYAK deal.
Over the last several weeks, we've received early conversion notices for about $390 million principal amount of our 2015 convertible notes, which we will settle in Q4 by issuing cash for the principal amount and shares of common stock for the conversion premium. Our cash and investments totaling about $6.6 billion at quarter close are available for general corporate purposes, including additional share repurchases, acquisitions, and debt repayment.
Now for fourth quarter 2013 guidance; we are forecasting total gross bookings to grow by 27% to 34% and to grow on a local currency basis by approximately 26% to 33%, with U.S. gross bookings growing by 17% to 24%. We expect international gross bookings expressed in U.S. dollars to grow by 29% to 36% and to grow on a local currency basis by approximately 28% to 35%.
Our Q4 forecast assumes that local currency ADRs for the consolidated group will be roughly flat compared to the prior year period. This reflects current trends as well as the mix impact in Q4 of high travel season and less mature Asian and South American markets that are typically lower ADR and less profitable than our more mature markets.