Western Hemisphere revenue increased by approximately $5 million, or 8%, during the fourth quarter of 2019 compared to the third quarter due to increased product and aftermarket revenue. Eastern Hemisphere revenue decreased by approximately $4 million, or 14%, as compared to the prior quarter due to lower product sales partially offset by higher fabricated joint work. Asia-Pacific revenue was flat sequentially.
Gross operating margin for the fourth quarter of 2019 was 30%, in line with the third quarter of 2019. For the full year of 2019, gross operating margin was 29%, which was up from 24% in the full year of 2018, driven by the improvements captured in the costs saving initiatives.
Cost of sales for the fourth quarter of 2019 was $75.7 million, a slight decrease of $0.3 million compared to the prior quarter. For the full year of 2019, cost of sales was $295 million, an increase of $1.4 million, or 0.5%, compared to full year 2018 cost of sales of $293.6 million.
Selling, General and Administrative Expenses
Selling, general and administrative (“SG&A”) expenses for the fourth quarter of 2019 were $21.4 million, a reduction of $6.6 million compared to third quarter of 2019, primarily due to lower stock compensation expense. For full year 2019, SG&A expenses decreased by approximately $4.3 million, or 4.3%, to $96.8 million from $101.1 million in 2018. The year-over-year reduction was primarily due to continued progress in the Company’s transformation efforts, partially offset by the return to more normalized annual merit increases for our employees. SG&A expenses as a percentage of revenues decreased to 23.3% for the year ended December 31, 2019, down from 26.3% for 2018.
Net Income, Adjusted EBITDA and Free Cash Flow
For the fourth quarter of 2019, Dril-Quip reported net income of $7.4 million, or $0.21 per diluted share, compared to a net loss of $1.3 million, or $0.04 per diluted share, in the third quarter of 2019. Adjusted net income for the fourth quarter was $8.1 million, or $0.23 per diluted share, after excluding $0.02 per share related to restructuring charges, gains related to foreign currency, the sale of assets, and other items. For the full year 2019, Dril-Quip reported net income of $1.7 million, or $0.05 per diluted share, compared to a net loss of $95.7 million, or $2.58 per diluted share, in 2018. Adjusted net income for the full year 2019 was $2.7 million, or $0.08 per diluted share, compared with an adjusted net loss of $23.5 million, or $0.63 per diluted share, in calendar 2018.
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