December 31, 2018, our Water Services, Water Infrastructure, Oilfield Chemicals and Other segments constituted 58.7%, 15.0%, 17.0% and 9.3% of our total revenue, respectively, compared to 60.5%, 23.6%, 6.0% and 9.9%, respectively, for the year ended December 31, 2017. The revenue increase by operating segment was as follows:
Water Services. Revenue increased $477.9 million, or 114.1%, to $896.8 million for the year ended December 31, 2018 compared to $418.9 million for the year ended December 31, 2017. The increase was primarily attributable to the Rockwater Merger as well as an increase in the demand for our services as a result of a rise in well completion count of 25.4% and an increase in the twelve month average U.S. land rig count of 18.4% during the year ended December 31, 2018 compared to the year ended December 31, 2017.
Water Infrastructure. Revenue increased $66.8 million, or 40.9%, to $230.1 million for the year ended December 31, 2018 compared to $163.3 million for the year ended December 31, 2017. The increase was primarily attributable to the Rockwater Merger as well as an increase in the demand for our services as a result of a rise in well completion count of 25.4% and an increase in the twelve month average U.S. land rig count of 18.4% during the year ended December 31, 2018 compared to the year ended December 31, 2017.
Oilfield Chemicals. Revenue from our Oilfield Chemicals segment of $259.8 million relates entirely to our Rockwater LLC operations acquired on November 1, 2017. Revenue increased $218.2 million, or 524.7%, to $259.8 million for the year ended December 31, 2018 compared to $41.6 million for the year ended December 31, 2017, primarily due to a full year of operations in 2018 versus two months of operations in 2017.
Costs of Revenue
Costs of revenue increased $695.7 million, or 109.6%, to $1.3 billion for the year ended December 31, 2018 compared to $634.7 million for the year ended December 31, 2017. The increase was largely attributable to the Rockwater Merger, higher labor costs due to an increase in employee headcount and outside services and higher rentals and materials expense as a result of increased demand for our services due to the overall increase in drilling, completion and production activities. The cost of revenue increase by operating segment was as follows:
Water Services. Costs of revenue increased $364.3 million, or 114.8%, to $681.5 million for the year ended December 31, 2018 compared to $317.3 million for the year ended December 31, 2017. The increase was primarily due to a full year of Rockwater operations in 2018 versus two months of operations in 2017 as well as organic growth revenue due to higher demand for our services.
Water Infrastructure. Costs of revenue increased $39.6 million, or 32.8%, to $160.1 million for the year ended December 31, 2018 compared to $120.5 million for the year ended December 31, 2017. The increase was primarily due to a full year of Rockwater operations in 2018 versus two months of operations in 2017 as well as organic growth due to higher demand for our services.
Oilfield Chemicals. Costs of revenue from our Oilfield Chemicals segment relates entirely to our Rockwater LLC operations acquired on November 1, 2017. Costs of revenue increased $196.4 million, or 530.5%, to $233.5 million for the year ended December 31, 2018 compared to $37.0 million for the year ended December 31, 2017, primarily due to a full year of operations in 2018 versus two months of operations in 2017. These costs primarily related to an increase in raw material costs incurred in manufacturing our chemical products.
Depreciation and Amortization. Depreciation and amortization expense increased $28.9 million, or 28.4%, to $130.5 million for the year ended December 31, 2018 compared to $101.6 million for the year ended December 31, 2017. The increase was primarily attributable to additional depreciation from assets acquired in the Rockwater Merger, which closed on November 1, 2017.
Gross Profit
Gross profit increased by $140.7 million, to a gross profit of $198.5 million for the year ended December 31, 2018 compared to a gross profit of $57.8 million for the year ended December 31, 2017 as a result of factors described above. Gross profit as a percent of revenue increased 4.7% to 13.0% during the year ended December 31, 2018, from