Support Services reported operating income of $3.3 million for the second quarter of 2022 compared to an operating loss of $2.4 million for the second quarter of 2021.
Cost of revenues. Cost of revenues increased 79.0 percent to $260.9 million for the three months ended June 30, 2022 compared to $145.8 million for the three months ended June 30, 2021. Cost of revenues increased primarily due to increases in expenses consistent with higher activity levels, such as materials and supplies expenses, maintenance and repairs expenses, employment costs and fuel costs. In addition, these costs increased due to higher market prices for materials and supplies, fuel and other raw materials. Cost of revenues as a percentage of revenues decreased primarily due to leverage of direct costs over higher revenues as well as improved pricing for our services.
Selling, general and administrative expenses. Selling, general and administrative expenses increased to $35.9 million for the three months ended June 30, 2022 compared to $29.4 million for the three months ended June 30, 2021, primarily due to increases in employment related costs. Selling, general and administrative expenses decreased from 15.6 percent of revenues in the second quarter of 2021 to 9.6 percent of revenues in the second quarter of 2022 due to leverage of costs that are relatively fixed during the short term over higher revenues.
Depreciation and amortization. Depreciation and amortization increased 12.3 percent to $20.1 million for the three months ended June 30, 2022, compared to $17.9 million for the three months ended June 30, 2021. Depreciation and amortization increased due to capital expenditures in the past year.
Gain on disposition of assets, net. Gain on disposition of assets, net was $1.8 million for the three months ended June 30, 2022 compared to a gain on disposition of assets, net of $3.1 million for the three months ended June 30, 2021. The gain on disposition of assets, net is generally comprised of gains and losses related to various property and equipment dispositions or sales to customers of lost or damaged rental equipment.
Other income, net. Other income, net was $79 thousand for the three months ended June 30, 2022 compared to other income, net of $616 thousand for the same period in the prior year.
Interest expense. Interest expense was $222 thousand for the three months ended June 30, 2022 compared to $103 thousand for the three months ended June 30, 2021. The increase in interest expense is primarily due to interest related to the finance lease that began in the third quarter of 2021. Interest expense also includes facility fees on the unused portion of the credit facility and the amortization of loan costs.
Income tax provision. Income tax provision was $13.5 million during the three months ended June 30, 2022 compared to $33 thousand for the same period in 2021. The effective tax rate was 22.3 percent for the three months ended June 30, 2022 compared to 4.8 percent for the three months ended June 30, 2021. The increase in the 2022 effective tax rate is primarily due to an increase in pre-tax income coupled with unfavorable permanent adjustments, partially offset by incrementally favorable discrete adjustments.
SIX MONTHS ENDED JUNE 30, 2022 COMPARED TO SIX MONTHS ENDED JUNE 30, 2021
Revenues. Revenues of $660.1 million for the six months ended June 30, 2022 increased 77.8 percent compared to the six months ended June 30, 2021. Domestic revenues of $644.2 million increased 107.5 percent for the six months ended June 30, 2022 compared to the same period in the prior year. The increase in revenues was due to higher customer activity levels, pricing improvements and a larger fleet of pressure pumping equipment in service. International revenues of $16.0 million decreased 29.3 percent for the six months ended June 30, 2022 compared to the same period in the prior year.
During the first six months of 2022, the average price of oil was 63.5 percent higher and the average price of natural gas was 85.1 percent higher, both as compared to the same period in the prior year. Oil and gas prices are higher due to continued strong demand as well as supply constraints worldwide due to the Russian invasion of Ukraine during the first quarter of 2022. The average domestic rig count during the first six months of 2022 was 59.5 percent higher than the same period in 2021.
The Technical Services segment revenues for the first six months of 2022 increased by 78.5 percent compared to the same period of the prior year due to higher activity levels and improved pricing. Technical Services reported operating income of $81.6 million during the first six months of 2022 compared to an operating loss of $4.3 million during the first six months of 2021. The Support Services segment revenues for the first six months of 2022 increased by 66.7 percent compared to the same period in the prior year,