Cost of sales (excluding depreciation, depletion and accretion) related to product revenue decreased by $17.8 million to $71.0 million for the three months ended September 30, 2025, as compared to $88.8 million for the three months ended September 30, 2024. This decrease was due to a decrease in rental equipment and outside service cost associated with lower production, as well as not incurring costs related to the temporary loadout equipment associated with the mechanical fire at the Kermit facility that occurred in 2024.
Cost of sales (excluding depreciation, depletion and accretion expense) related to services decreased by $18.7 million to $117.8 million for the three months ended September 30, 2025, as compared to $136.5 million for the three months ended September 30, 2024. The decrease was due to shortened average drive distances for deliveries to last-mile logistics customers during the period.
Cost of sales (excluding depreciation, depletion, and accretion expense) related to rentals is $6.4 million for the three months ended September 30, 2025, due to the acquisition of Moser and the cost of sales associated with leasing power equipment. There was no cost of sales related to rentals for the three months ended September 30, 2024.
Depreciation, depletion and accretion expense. Depreciation, depletion and accretion expense increased by $14.5 million to $40.6 million for the three months ended September 30, 2025, as compared to $26.1 million for the three months ended September 30, 2024, due to additional depreciable assets placed into service when compared to the prior period as well as contribution from Moser and PropFlow.
Selling, general and administrative expense. Selling, general and administrative expense increased by $10.8 million to $36.3 million for the three months ended September 30, 2025, as compared to $25.5 million for the three months ended September 30, 2024. The increase is due to an increase of $3.0 million from stock-based compensation, an increase of $3.7 million in other corporate expenses, as well as $4.1 million contribution from Moser for the three months ended September 30, 2025, compared to the three months ended September 30, 2024.
Our selling, general and administrative expense includes the non-cash expense for stock-based compensation expense for equity awards granted to our employees. For the three months ended September 30, 2025, stock-based compensation expense was $9.3 million, as compared to $6.3 million of stock-based compensation expense for the three months ended September 30, 2024.
Amortization expense of acquired intangible assets. Amortization expense of acquired intangible assets increased $2.2 million to $5.9 million for the three month ended September 30, 2025, as compared to $3.7 million for the three month ended September 30, 2024. The increase was primarily due to the amortization of intangibles associated with the Moser Acquisition and PropFlow Acquisition.
Loss on disposal of assets. There was no loss on disposal of assets for the three months ended September 30, 2025, as compared to $8.6 million loss on disposal of assets for the three months ended September 30, 2024, due to the $8.6 million disposal from the damaged dredge asset. See Note 6 - Property, Plant and Equipment, Net - Impairment or Disposal of Long-Lived Assets for more information.
Interest (expense), net. Interest expense, net increased by $3.8 million to $15.0 million for the three months ended September 30, 2025, as compared to $11.2 million for the three months ended September 30, 2024. The increase is driven by the 2025 Term Loan Credit Facility and associated debt refinancing.
Income tax expense (benefit). Income tax expense (benefit) decreased by $10.2 million to $(9.8) million for the three months ended September 30, 2025, as compared to $0.4 million for the three months ended September 30, 2024. The decrease is primarily attributable to a decrease in income before income taxes for the three months ended September 30, 2025 as compared to the three months ended September 30, 2024.
Nine Months Ended September 30, 2025 Compared to Nine Months Ended September 30, 2024
Product Revenue. Product revenue decreased by $14.2 million to $372.8 million for the nine months ended September 30, 2025, as compared to $387.0 million for the nine months ended September 30, 2024. A decrease in proppant prices between the periods contributed to a $77.6 million decrease in product revenue. This was partially offset by an increase in sales volume which contributed to a $39.5 million increase in product revenue. Additionally, there was $23.9 million in shortfall revenue for the nine months ended September 30, 2025, as compared to no shortfall revenue for the nine months ended September 30, 2024.
Service Revenue. Services revenue, which includes freight for last-mile logistics services, increased by $35.0 million to $432.6 million for the nine months ended September 30, 2025, as compared to $397.6 million for the nine months ended September 30, 2024. The increase in logistics revenue was due to higher sales volumes shipped to last-mile logistics customers.
Rental Revenue. Rental revenue is $40.4 million for the nine months ended September 30, 2025, due to the acquisition of Moser and the related revenue from leasing power equipment. There was no rental revenue for the nine months ended September 30, 2024.
Cost of sales (excluding depreciation, depletion and accretion expense). Cost of sales (excluding depreciation, depletion and accretion expense) increased by $63.0 million to $597.2 million for the nine months ended September 30, 2025, as compared to $534.2 million for the nine months ended September 30, 2024.