sales to government and defense customers decreased to 14.6% from 18.5% as the gross profit margin on these recent contract awards is lower than our existing government and defense activity.
Gross profit on sales to commercial customers increased $10.7 million or 25.0% over the prior year period primarily due to the increased volume and improved profitability in our MRO activities. The gross profit margin on sales to commercial customers increased from 14.0% to 16.2% primarily from the increased profitability in our MRO activities.
Expeditionary Services Segment
Sales in the Expeditionary Services segment increased $1.8 million or 6.5% over the prior year period primarily due to stronger demand for our mobility products.
Gross profit in the Expeditionary Services segment decreased $2.5 million or 61.0% from the prior period primarily due to higher material costs. Gross profit margin decreased to 5.4% from 14.7% primarily as a result of these higher costs.
Selling, General and Administrative Expenses
Selling, general and administrative expenses increased $9.9 million over the prior year period. As a percent of sales, selling, general and administrative expenses increased to 10.7% from 10.3% in the prior year period. These increases are primarily attributable to investigation and remediation compliance costs of $2.8 million and severance costs of $0.8 million.
Income Taxes
Our effective income tax rate for continuing operations was 16.6% for the first quarter of fiscal 2020 compared to 10.8% in the prior year period. Higher excess tax benefits from the vesting of restricted shares and stock options exercises in fiscal 2019 compared to the current year period drove the higher effective tax rate in fiscal 2020. We recognized $2.5 million of excess tax benefits as a reduction to income tax expense during the first quarter of fiscal 2019 compared to $1.4 million in the current year period.
Liquidity, Capital Resources and Financial Position
Our operating activities are funded and commitments met through the generation of cash from operations. In addition to operations, our current capital resources include an unsecured Revolving Credit Facility and an accounts receivable financing program. Periodically, we may also raise capital through common stock and debt financings in the public or private markets. We continually evaluate various financing arrangements, including the issuance of common stock or debt, which would allow us to improve our liquidity position and finance future growth on commercially reasonable terms. Our continuing ability to borrow from our lenders and issue debt and equity securities to the public and private markets in the future may be negatively affected by a number of factors, including the overall health of the credit markets, general economic conditions, airline industry conditions, geo-political events, and our operating performance. Our ability to generate cash from operations is influenced primarily by our operating performance and changes in working capital.
At August 31, 2019, our liquidity and capital resources included cash of $39.9 million and working capital of $625.2 million.
We maintain a Revolving Credit Facility with various financial institutions, as lenders, and Bank of America, N.A., as administrative agent for the lenders. On September 25, 2019, we entered into an amendment to our Revolving Credit Facility which extended the maturity of the Revolving Credit Facility to September 25, 2024, increased the revolving credit commitment to $600 million, and modified certain other provisions. Under certain circumstances, we have the ability to request an increase to the revolving credit commitment by an aggregate amount of up to $300 million, not to exceed $900 million in total.