For the three months ended December 31, 2018, revenue increased $13 million in the Imagery segment driven largely by growth in the segment's US Government business and by the inclusion of revenues from the DigitalGlobe Imagery business, which added four additional selling days in the quarter. 

Revenues from the Imagery segment increased $615 million in 2018 compared to 2017. The increase was primarily driven by the inclusion of DigitalGlobe's imagery business for a full year compared to only one quarter of results in 2017. During this period DigitalGlobe's imagery business drove an increase in revenues of $613 million to the Imagery segment before intercompany eliminations. Excluding revenue from DigitalGlobe's imagery business, revenue from the Imagery segment before intercompany eliminations increased $2 million period over period.

In the fourth quarter of 2018, adjusted EBITDA margin percentage from the Imagery segment decreased from 63.5% to 57.3%. The decrease is primarily related to revenue mix and higher costs.

Adjusted EBITDA margin percentage from the Imagery segment for 2018 was 61.3%, compared to 62.2% in 2017. The decrease in margin percentage reflected the blend of margins from DigitalGlobe's imagery business for a full year as compared with only approximately three months in 2017.

Services Results

For the three months ended December 31, 2018, revenue increased $5 million in the Services segment.  Revenue increased due to growth from new contract awards and the expansion of programs in the Department of Defense and the Intelligence Community, as well from the inclusion of revenues from the DigitalGlobe businesses, which added four additional selling days in the quarter. The increase in revenue was partially offset by a decrease in production on GEOINT Production work year over year.

Services segment revenue increased $122 million in 2018 compared to the same period in 2017. The increase was primarily driven by the inclusion of DigitalGlobe's services business for a full year compared to only one quarter of results in 2017. The inclusion of the DigitalGlobe's services business drove an increase in revenues of $112 million year over year before intercompany eliminations. Excluding the revenue from the DigitalGlobe Transaction, the Services segment revenue increased $10 million period over period.

In the fourth quarter of 2018, adjusted EBITDA margin percentage from the Services segment decreased from 15.9% to 8.8%. The decrease is primarily driven by GEOINT Production work being down significantly in the three months ended December 31, 2018 as compared to the same period of 2017.

Adjusted EBITDA margin percentage from the Services segment for 2018 was 9.4%, compared to 16.0% in 2017. The decrease in margin percentage reflected the blend of margins from DigitalGlobe's services business for a full year as compared with only approximately three months in 2017.

Revenue and Adjusted EBITDA by Segment

The following table summarizes revenue and adjusted EBITDA by segment quarterly for 2018 and year to date 2017 and 2016, in U.S. dollars.