In 2019, we continued to focus our efforts on reducing and removing the health and safety (H&S) risks associated with our activities. Various initiatives were carried out regionally and globally to ensure that H&S remained front of mind for employees by means of visible safety leadership, regular communications and training, resulting in fewer employees being exposed to harm in our business on our journey to Zero Harm.
Our reputation depends on our ability to be outstanding professionals, acting with honesty, integrity, and transparency in our daily dealings with colleagues, clients, and other business partners. During the past year, our Ethics & Compliance team helped sustain a continuous spotlight on ethics, by working to embed principled decision-making into key processes and initiatives. To deepen the discussion on ethical risks with senior leadership, as well as on ethics as the foundation of all sustainability initiatives, our ethics roadshows continued on a larger scale in 2019, involving 16 offices across Europe, Latin America, Africa, Asia, Australia and the Middle East. For 2020, additional roadshows are underway and planned throughout the year.
At WSP, we take our responsibility for sustainable leadership very seriously, not only in the advice we provide to our clients but also in our own operations. As part of our Global Strategic Plan, we announced our objective for a 25% reduction in absolute, market-based greenhouse gas emissions across our global operations from 2018 to 2030, with an interim reduction target of 5% by 2021. This is a serious commitment, and in 2019, we set up an internal Task Force to achieve these reduction targets, comprised of key regional and global leadership. Last April, we joined the United Nations Global Compact (UNGC), committing to set in motion changes to our business operations, corresponding to the UNGC’s Ten Principles. Challenging the status quo is part of who we are as an organization, and recently we did just that by becoming the first professional services firm in the Americas to formally link sustainability-linked terms and financing through a syndicated credit facility.
This past year we were faced with various turbulent political and market realities. However, the strength of our operating model, coupled with our ability to be agile and responsive, allowed us to achieve solid financial performance for 2019, while delivering significant return to our shareholders. Highlights include 14.4% growth in our net revenues, which stood at $6.9 billion for the year. In line with our 2019 outlook, consolidated organic growth in net revenues stood at 3.5%, spanning across all reportable segments. In addition to our backlog of $8.1 billion, representing 10.6 months of revenues, we reported an adjusted EBITDA of $1 billion and adjusted EBITDA margin of 15.1%, reaching the high end of the 2019 guidance provided.
In terms of other metrics, we were pleased to report that days sales outstanding (DSO) continued to decrease and reached 74 days at the end of 2019, a two-day improvement compared to 2018. Our free cash flow for the year came in at $441.6 million or 154% of net earnings, beyond our cash flow conversion target of 100% of net earnings.
In tandem with our strong balance sheet, these results place us on solid footing for 2020, and favourably position us to meet our 2019-2021 Global Strategic Plan financial ambitions.