Welcome and thank you for standing by. At this time, all participants are in a listen-only mode. Today's conference is being recorded. If you have any objections, you may disconnect at this time.
Now I will turn the meeting over to Ms. Patricia Murphy with IBM. Ma'am, you may begin.
Thank you. This is Patricia Murphy, Vice President of Investor Relations for IBM. And I want to welcome you to our Fourth Quarter 2019 Earnings Presentation. I'm here with Jim Kavanaugh, IBM's Senior Vice President and Chief Financial Officer. We'll post today's prepared remarks on the IBM Investor website within a couple of hours and a replay will be available by this time tomorrow.
Some comments made in this presentation may be considered forward-looking under the Private Securities Litigation Reform Act of 1995. These statements involve factors that could cause our actual results to differ materially. Additional information about these factors is included in the company's SEC filings.
Our presentation also includes non-GAAP measures to provide additional information to investors. For example, consistent with last quarter's format, we present revenue growth at constant currency throughout the presentation. In addition to provide a view consistent with our go-forward business, we'll focus on constant currency growth adjusting for the divested businesses for the impacted lines of total revenue, cloud and our geographic performance. We have provided reconciliation charts for these and other non-GAAP measures at the end of the presentation and in the 8-K submitted to the SEC.
I also want to remind you that IBM's revenue, profit and earnings per share reflect the impact of purchase accounting and other transaction-related adjustments associated with the acquisition of Red Hat. These adjustments and charges are primarily non-cash.
So with that, I'll turn the call over to Jim.
James J. Kavanaugh
Thanks, Patricia. And thanks to all of you for joining us.
We had a solid finish to 2019. In the fourth quarter, we grew revenue at actual rates and it was up 3% at constant currency excluding divestitures. Our operating gross margin was up over 2 points, which is the best margin expansion in some time. We delivered $4.2 billion of operating net income and $6 billion of free cash flow, and we had $4.71 of operating earnings per share. We also reduced our debt balance by another $3 billion in the quarter for a total reduction of $10 billion since the end of June. This caps off a year with $77 billion of revenue, $12.81 of operating earnings per share, and about $12 billion of free cash flow, in line with our expectations.
In 2019, we took a number of actions to strengthen our foundation for the next chapter of our clients' digital reinventions. We acquired Red Hat with a number one Linux operating system, RHEL, and the leading hybrid cloud platform OpenShift. We modernized our software portfolio, making it cloud-native and optimized for OpenShift. We announced the industry's first public cloud designed specifically for financial services. We expanded our services offerings and skills for the