in 2024 was primarily due to the $3.1 million benefit accrued for the probable recovery of attorney fees related to the silo failure litigation developments, as discussed in Note 7 of Part I, Item 1, which is not indicative of future SG&A expenses.
Other income (expense), net. Other income, net was $2.6 million for the three months ended June 30, 2024, which was primarily related to $2.2 million recovery of previously incurred demurrage and other transportation-related matters. Other income, net was $2.5 million for the same period in 2023, which was primarily due to $1.9 million of insurance proceeds received in excess of the Berwind ignition recovery asset accrued in 2022. These activities are not indicative of future results.
Interest expense, net. Interest expense, net was $1.5 million for the three months ended June 30, 2024 compared to $2.5 million for the same period in 2023. The decrease in 2024 was largely due to the repayment in full of related-party debt in 2023 associated with the financing of the acquisition of Ramaco Coal from Yorktown Partners. Interest expense related to this financing was $0.6 million in the second quarter of 2023.
Income tax expense. The effective tax rate for the three months ended June 30, 2024 and June 30, 2023 was 26.3% and 24.6%, respectively, excluding the $0.8 million favorable impact of discrete items. The primary differences from the federal statutory rate of 21% are related to state taxes, non-deductible expenses, the foreign-derived intangible income deduction, and depletion expense for income tax purposes.
Earnings per share. Refer to Note 10 of Part I, Item 1 for information regarding earnings per share calculations for Class A and Class B common stock.
Six Months Ended June 30, 2024 Compared to Six Months Ended June 30, 2023
Revenue. Coal sales revenue for the six months ended June 30, 2024 was $328.0 million, approximately 8% higher than the same period in 2023 driven by the 25% increase in tons sold offset partially by the negative impact of pricing. The increase in tons sold occurred in both North America and export markets, with North America volumes increasing by 27% and export volumes increasing by 24%, and was aided by the Company’s increased capacity for production achieved during late 2023. Revenue per ton sold decreased 14% from $206 per ton for the six months ended June 30, 2023 to $178 per ton for the six months ended June 30, 2024 and was driven by the variability in index-based pricing for export sales. Revenue per ton sold (FOB mine), a non-GAAP measure which excludes transportation revenues and demurrage, decreased 15% from $176 per ton for the six months ended June 30, 2023 to $149 per ton for the six months ended June 30, 2024. U.S. coal price indices have fallen by roughly 25% on a year-to-date basis driven by the macroeconomic conditions discussed earlier. We expect metallurgical coal prices to remain volatile in the near term.
There are no revenues from rare earth and critical minerals at this time.
Cost of sales. Our cost of coal sales totaled $262.5 million for the six months ended June 30, 2024 compared to $209.7 million for the same period in 2023. The 25% increase was driven by the increase in tons sold, as discussed directly above. Cost of sales per ton sold decreased 1% from $143 per ton for the six months ended June 30, 2023 to $142 per ton for the six months ended June 30, 2024. Cash cost per ton sold (FOB mine), a non-GAAP measure which excludes transportation costs, alternative mineral development costs, and idle mine costs, increased 3% from $110 per ton for the six months ended June 30, 2023 to $113 per ton for the six months ended June 30, 2024. Mine costs for 2024 were impacted negatively by challenging geology and labor constraints in the first quarter of 2024 but improved during the second quarter of 2024 as discussed previously.
Depreciation, depletion, and amortization. Depreciation, depletion, and amortization expense totaled $31.1 million and $25.4 million for the six months ended June 30, 2024 and June 30, 2023, respectively. The increase year-to-year occurred across all asset types and was driven by the Company’s initiative to grow production.
Selling, general, and administrative. Selling, general, and administrative (“SG&A”) expenses were $25.0 million and $26.1 million for the six months ended June 30, 2024 and June 30, 2023, respectively. The decrease in 2024 is due