Strong execution across our facilities, including the recently acquired EQ operations, delivered better than anticipated results in the third quarter of 2014. Continued strong organic growth in our legacy project-based Event Business and recurring Base Business combined with strong EQ results in the first full quarter of ownership led to revenue more than doubling to $290.3 million in the first nine months of 2014 versus the year ago period. Operating income increased 42% to $53.3 million and includes $5.6 million of EQ acquisition related costs. Adjusted EBITDA for the first nine months of 2014 was $77.9 million, up 53%, with adjusted earnings per diluted share growing 24% to $1.60.
On the strength of the fundamental business in both the legacy US Ecology and the acquired EQ operations, we revised our full year guidance upward for the third time in 2014. We now expect annual adjusted earnings per share to range from $1.92 to $1.97 per share and adjusted EBITDA to range from $110 million to $115 million, up from $1.70 to $1.80 and $200 to $110 million, respectively. These increased estimates exclude foreign currency translation gains or losses and business development and integration expenses.
I couldn't be more pleased with the collective effort of the team as we move ahead as a combined company. Our integration activities are progressing on schedule and with each day that passes, we are becoming a more unified team with a common goal to bring best in class customer service and solutions to the industry. Our national footprint, cross-selling opportunities and other operational cost efficiencies will drive synergies in the months and years to come.
Looking out to 2015 and beyond, we continue to see a strong pipeline of opportunities and no fundamental change to our growth drivers. We will continue to leverage this unique combination of high quality treatment and disposal assets and complementary field and industrial services provided by the acquisition of EQ. Together we are a true industry leader and our outlook is greater than it has ever been. We look forward to continuing to deliver sustainable solutions for our customers and long-term value for our stockholders.
President and Chief Executive Officer