Cactus Inc (NYSE: WHD) company’s profitability during the fourth quarter was generally consistent with the company expectations despite the dramatic decline in oil prices throughout the fourth quarter, and we were pleased with the resiliency demonstrated by our business. Drilling related activity showed a slight increase, while completions related revenue declined more than anticipated as customers deferred activity due to budget exhaustion. The overall margin profile of the business remained strong notwithstanding the more pronounced than usual seasonal slowdown in the Field Service and Other business.
As of December 31, 2018, the Company had $70.8 million of cash on hand, no bank debt outstanding and the full $75.0 million of capacity available under the Company’s revolving credit facility. Operating cash flow was $44.8 million for fourth quarter 2018 and $167.2 million for 2018, reflecting strong operating results. Net capital expenditures for fourth quarter 2018 were $13.7 million, driven largely by additions to the Company’s fleet of rental assets. Net capital expenditures for 2018 were $68.2 million.
Moreover, fourth quarter 2018 product revenue decreased $0.5 million, or 0.6%, sequentially, as lower sales of production related equipment more than offset an increase in sales of wellhead equipment. Gross profit increased $0.6 million sequentially with margins improving 100 basis points primarily due to product mix and more favorable supply chain execution. Fourth quarter 2018 rental revenue decreased $6.9 million, or 18.2%, sequentially, as budget exhaustion and the steep decline in oil prices during the quarter led to reduced customer completion activity. Gross profit decreased $5.1 million sequentially with gross profit margins down 320 basis points, primarily due to depreciation expense representing a higher proportion of revenue than during the previous quarter. Fourth quarter 2018 field service and other revenue decreased $3.4 million, or 10.3%, sequentially, as lower completion activity coupled with fourth quarter seasonality drove a decline in associated billable hours and ancillary services. Gross profit decreased $4.2 million sequentially due to lower labor utilization during the quarter.
Additionally, SG&A for fourth quarter 2018 was $10.5 million (7.5% of revenues), compared to $6.6 million (6.3% of revenues) for fourth quarter 2017. The sequential decrease is primarily related to lower professional and legal fees.
For the first quarter of 2019, the company currently anticipate that revenue across all the business lines will increase relative to the fourth quarter of 2018 based on the rebound in activity the company have seen during the first two months of the year. For the full year 2019, the company expects capital expenditures to be in the range of $60 to $65 million.