13% and 8% for the three months ended September 30, 2020 and 2019, respectively and was 10% and 7% for the nine months ended September 30, 2020 and 2019, respectively.
System Services
System services revenue decreased $7.3 million, or 40%, to $10.9 million for the three months ended September 30, 2020 compared to $18.2 million for the three months ended September 30, 2019. System services revenue decreased $13.4 million, or 28%, to $35.2 million for the nine months ended September 30, 2020 compared to $48.6 million for the nine months ended September 30, 2019. System services revenue decreased due to a decrease in services provided to coordinate proppant delivered into our systems, as well as a decrease in mobile proppant systems on a fully utilized basis.
Cost of system services decreased $7.9 million, or 38%, to $13.1 million for the three months ended September 30, 2020 compared to $21.1 million for the three months ended September 30, 2019, excluding depreciation and amortization expense. Cost of system services decreased $13.1 million, or 23%, to $43.3 million for the nine months ended September 30, 2020 compared to $56.4 million for the nine months ended September 30, 2019, excluding depreciation and amortization expense. Cost of system services decrease in services provided to coordinate proppant delivered to systems as well as a decrease in field support activity and third-party trucking services required to support fewer fully utilized systems. Cost of system services as a percentage of system services revenue was 121% and 116% for the three months ended September 30, 2020 and 2019, respectively and was 123% and 116% for the nine months ended September 30, 2020 and 2019, respectively.
Transloading Services
Transloading services revenue decreased $4.1 million, or 93%, to $0.3 million for the three months ended September 30, 2020 compared to $4.4 million for the three months ended September 30, 2019. Transloading services revenue decreased $14.1 million, or 93%, to $1.0 million for the nine months ended September 30, 2020 compared to $15.1 million for the nine months ended September 30, 2019. This decrease was primarily due to recognition of $3.2 million and $9.5 million of deferred revenue in the three and nine months ended September 30, 2019, respectively, as well as a decrease in the number of tons transloaded.
Selling, General and Administrative Expenses
Selling, general and administrative expenses decreased $1.1 million, or 22%, to $3.8 million for the three months ended September 30, 2020 compared to $4.9 million for the three months ended September 30, 2019, excluding depreciation and amortization. Selling, general and administrative expenses decreased $1.8 million, or 13%, to $12.2 million for the nine months ended September 30, 2020 compared to $14.0 million for the nine months ended September 30, 2019, excluding depreciation and amortization. The decrease is due primarily to cost cutting measures, including headcount, salary and support cost reductions, in response to the reduction in industry activity.
Impairment Losses
As a result of risks and uncertainties associated with volatility in global oil markets driven by significant reductions in demand for oil due to COVID-19 and certain actions by oil producers globally and the expected impact on our businesses, operations, earnings and results, we recorded impairment losses and other charges of $37.8 million, $4.2 million, $2.8 million, $2.6 million and $0.4 million in relation to property, plant and equipment, goodwill, ROU assets, inventories and other assets, respectively, in the nine months ended September 30, 2020.
Provision for Income Taxes
During the three months ended September 30, 2020, we recognized a combined United States federal and state benefit for income taxes of $0.8 million, an increase of $4.5 million as compared to the $3.7 million income tax expense we recognized during the three months ended September 30, 2019. During the nine months ended September 30, 2020, we recognized a combined United States federal and state benefit for income taxes of $8.2 million, an increase of $20.2 million as compared to the $12.0 million income tax expense we recognized during the nine months ended September 30, 2019. This change was attributable to lower operating income. The effective combined United States federal and