Adjusted earnings per share totaled $1.30, up 34% year-over-year, marking the best third quarter in our company's history.
Net revenues totaled a record $1.8 billion and, on a pro forma basis, increased 11% versus last year, with all three of our business segments contributing to the strong year-over-year growth.
Total transaction revenues grew 13%, while total recurring revenues, which accounted for nearly half of our business, increased by 10%.
Third quarter adjusted operating expenses totaled $755 million, including $35 million related to Bakkt, which, after successfully completing its merger with Victory Park, recently began trading on the NYSE.
Adjusting for Bakkt, third quarter operating expenses would have been $720 million, in the middle of our guidance range, while operating -- or while our adjusted operating margin would have been 60%, up over 100 basis points year-over-year.
Looking to the fourth quarter, we expect adjusted operating expenses to be between $737 million to $747 million.
Relative to the full year outlook provided on our second quarter call, the fourth quarter is now expected to include approximately $10 million related to the Bakkt stub period and $10 million to $15 million of performance-related compensation as we expect to reward our employees for their contribution to the strong results we are once again on track to achieve in 2021.
Record year-to-date free cash flow has totaled nearly $2 billion.
These strong cash flows, along with the divestment of our $1.2 billion stake in Coinbase, has enabled us to reduce leverage to under 3.25 times at the end of September, nearly a full year ahead of schedule.
As a result, we expect to resume share repurchases, including up to $250 million in this year's fourth quarter.
In addition, we announced in October that we have agreed to sell our stake in Euroclear for EUR709 million or approximately $820 million.
Third quarter net revenues totaled $959 million, an increase of 16% year-over-year.
This strong performance was driven by a 30% increase in our interest rate business and a 38% increase in our energy revenues, including 34% increase in our oil complex, a 73% increase in European natural gas revenues and a 72% increase in revenues related to global environmental products.
Importantly, total open interest, which we believe to be the best indicator of long-term growth, is up 18% versus the end of last year, including 11% growth in energy and 28% growth across our financial futures and options complex.
Recurring revenues, which include our exchange data services and NYSE listings, increased 6% year-over-year, including 10% growth in our listings business.
Looking to the fourth quarter, we expect recurring revenues in our Exchange segment to be between $330 million and $335 million.
Third quarter revenues totaled $477 million, a 6% increase versus a year ago.
Recurring revenue growth, which accounted for nearly 90% of segment revenues, also grew 6% in the quarter.
Within recurring revenues, our fixed income, data and analytics business increased by 5% year-over-year, including another double-digit growth in our index franchise, while other data and network services grew 9% driven by continued customer demand for additional network capacity.
Looking to the fourth quarter, we expect that our recurring revenues will improve sequentially to a range of $415 million to $420 million and that full year revenue growth will be approximately 6%, at the high end of our guidance range.
Despite a double-digit decline in industry origination volumes, our Mortgage Technology business grew 7% year-over-year and achieved record revenues of $366 million.
While third quarter transaction revenues declined slightly, they were more than offset by a 33% growth in our recurring revenues, which, at $143 million, once again exceeded the high end of our guidance range and accounted for nearly 40% of total segment revenues.
While these secular growth trends have been a clear tailwind for our recurring revenues, there is also opportunity to drive accelerating adoption across our transaction-based businesses such as our closing solutions, where revenue increased by 30% in the third quarter.
Looking to the fourth quarter guidance, we expect that recurring revenues will once again grow sequentially and be in a range of $147 million to $152 million.
At the midpoint, this represents growth of approximately 25% year-over-year, which is on top of 20% growth achieved in last year's third quarter.
We also generated strong cash flows, reduced leverage to under 3.25 times, announced the divestment of our stake in Euroclear and successfully took back public on the NYSE.
And today, cleaner energy sources, including global natural gas and environmentals, make up approximately 40% of our energy revenues and have grown 12% on average over the past five years.
Revenues in our TTF markets have grown 38% on average over the last five years, including 84% growth in the third quarter.
Energy consumption is expected to double over the next 30 years, yet carbon emissions are expected to be reduced by half.
Our comprehensive offering and the efficiencies that it delivers positions us well to execute on what we believe to be a $1 billion opportunity.
Today, only a fraction of Mortgage Technology customers take our AIQ solution, and we continue to have strong sales success cross-selling to existing customers even if they're not on our loan origination system, including one of the largest depositories in the U.S. And while still an early opportunity at under $100 million in revenue today, the efficiencies that our data analytics provide position us well to continue executing against what we think is a $4 billion opportunity.
Flywheel effect that our leading technology and data provides, combined with the cross-sell that our broad connectivity offers, generates an array of opportunities for us to grow a business that at $1.4 billion today is only a fraction of the $10 billion opportunity.
It's collaborative efforts, innovative solutions and strategic capital allocation like this that have driven our growth for the past 20 years and which lay the foundation for continued growth well into the future.

Summary:
Adjusted earnings per share totaled $1.30, up 34% year-over-year, marking the best third quarter in our company's history.
Net revenues totaled a record $1.8 billion and, on a pro forma basis, increased 11% versus last year, with all three of our business segments contributing to the strong year-over-year growth.
Third quarter net revenues totaled $959 million, an increase of 16% year-over-year.
Looking to the fourth quarter, we expect recurring revenues in our Exchange segment to be between $330 million and $335 million.
Looking to the fourth quarter, we expect that our recurring revenues will improve sequentially to a range of $415 million to $420 million and that full year revenue growth will be approximately 6%, at the high end of our guidance range.
Looking to the fourth quarter guidance, we expect that recurring revenues will once again grow sequentially and be in a range of $147 million to $152 million.