Depreciation and amortization. Total depreciation and amortization expense for the three months ended September 30, 2025 was $15.4 million, an increase of $7.6 million from the three months ended September 30, 2024. The change was primarily due to additional depreciation for assets acquired related to our acquisitions.
Acquisition and integration costs. Acquisition and integration costs for the three months ended September 30, 2025 were $3.6 million, a decrease of $16.7 million from the three months ended September 30, 2024. The change was due to a reduction of costs incurred attributable to the Merger in 2024.
Interest expense. Total interest expense was $0.7 million for the three months ended September 30, 2025 and 2024. Interest expense is comparable during both periods due to similar average total debt and finance lease obligations during the comparative periods.
Other income. Total other income for the three months ended September 30, 2025 was $0.3 million, a decrease of $0.6 million from the three months ended September 30, 2024. The change was primarily due to the net change in our foreign currency exchange gains (losses).
Equity method earnings. Equity method earnings consist of the net earnings in DWS, along with the amortization of our proportional ownership interest in the step up of the fair value of the intangible assets acquired, during the period that DWS was accounted for as an equity method investee. With the purchase of the remaining 80% equity interest in DWS on November 29, 2024, we did not recognize equity method earnings in 2025. Total equity method earnings, excluding the amortization of the step up in fair value, for the three months ended September 30, 2024 was $1.4 million. The amortization of the step up in the fair value of the intangible assets acquired for the three months ended September 30, 2024 was $0.4 million.
Income tax expense. Our operations are subject to U.S. federal income tax at an entity level, as well as various state income and franchise taxes. In addition, our operations located in international jurisdictions are subject to local country income taxes. Income tax expense for the three months ended September 30, 2025 was $18.7 million, an increase of $21.3 million from the three months ended September 30, 2024. The change was primarily driven by changes in our mix of income before income taxes by geography and tax jurisdiction, discrete items recorded in the quarter, and other non-deductible expenses. For the three months ended September 30, 2025, income before income taxes was $58.0 million, a decrease of $22.0 million from the three months ended September 30, 2024.
Net income. Net income for the three months ended September 30, 2025 was $39.2 million, a decrease of $43.4 million from the three months ended September 30, 2024, as a result of both the gain on bargain purchase recognized for the three months ended September 30, 2024 and the factors discussed above.
Nine Months Ended September 30, 2025 Compared to Nine Months Ended September 30, 2024
Revenues. Our NAM market revenue for the nine months ended September 30, 2025 was $372.4 million, an increase of $114.0 million from the nine months ended September 30, 2024, primarily driven by an increase in market share and incremental business operations due to the acquisitions of DWS, SCF and Citadel. This was offset by a reduction in drilling activity in North America due to a decline in the North American onshore rig count during the comparative period. Our International and Offshore market revenue for the nine months ended September 30, 2025, was $332.2 million, an increase of $180.4 million from the nine months ended September 30, 2024, primarily driven by increased business operations due to the aforementioned acquisitions.
Cost of revenues, exclusive of depreciation and amortization. Total cost of revenues for the nine months ended September 30, 2025 was $480.5 million, an increase of $218.1 million from the nine months ended September 30, 2024. The change was attributable to a $77.5 million increase in personnel expense and an increase in our product costs due to an increase in sales activity.
Selling, general and administrative expenses. Selling, general and administrative expense for the nine months ended September 30, 2025 was $96.8 million, an increase of $18.9 million from the nine months ended September 30, 2024. The change was primarily attributable to an increase in salaries and wages, IT costs, R&D costs, and facilities expenses of $33.2 million driven by an increase in headcount and business activity attributable to the acquisitions of DWS, SCF and Citadel, offset by a decrease in bad debt of $14.5 million, including the recoveries of outstanding receivables from our prior agent in Saudi Arabia.
Gain on sale of assets. Gain on sale of assets for the nine months ended September 30, 2025 and 2024 was $41.2 million and $0.5 million, respectively. The change was driven by the sale of our Subsea Tree product line in June of 2025 and the Eldridge Facility assets in September of 2025, both of which resulted in a gain, offset by normal variations associated with the sale of property and equipment during the period.
Depreciation and amortization. Total depreciation and amortization expense for the nine months ended September 30, 2025 was $45.3 million, an increase of $26.1 million from the nine months ended September 30, 2024. The change was primarily due to additional depreciation for assets acquired related to our acquisitions.
Long-lived asset impairments. Long-lived asset impairment expense for the nine months ended September 30, 2025 was $3.4 million, a decrease of $0.1 million from the nine months ended September 30, 2024. The impairment expense was primarily related to (i) land and a building in Mexico acquired as part of the Merger that was held for sale at March 31, 2025 and marketed at an amount that was lower than the net book value, which ultimately resulted in an impairment expense of $2.9 million and (ii) declining market conditions associated with our anticipated sub-lease of the prior Dril-Quip corporate office.