32.9% of total revenues. For the three months ended March 31, 2019, we had revenues of $51.0 million, of which our Assessment, Permitting and Response segment generated $4.6 million, or 9.0% of total revenues, our Measurement and Analysis segment generated $28.3 million, or 55.6% of total revenues, and our Remediation and Reuse segment generated $18.1 million, or 35.4% of total revenues. Revenue from the Discontinued Service Lines of $1.0 million and $3.5 million for the three months ended March 31, 2020 and March 31, 2019, respectively, was all in our Remediation and Reuse segment.
Cost of Revenues
Cost of revenues consists of all direct costs required to provide services, including fixed and variable direct labor costs, equipment rental and other outside services, field and lab supplies, vehicle costs and travel- related expenses.
For the three months ended March 31, 2020, cost of revenues was $44.4 million or 72.7% of revenues, and was comprised of direct labor of $27.4 million, outside services (including construction, laboratory, shipping and freight and other outside services) of $9.3 million, field supplies, testing supplies and equipment rental of $4.3 million, project-related travel expenses of $1.6 million and other direct costs of $1.8 million. For the three months ended March 31, 2020, cost of revenues as a percentage of revenue was relatively unchanged compared to the prior year period.
For the three months ended March 31, 2019, cost of revenues was $37.1 million or 72.8% of revenues, and was comprised of direct labor of $22.0 million, outside services (including construction, laboratory, shipping and freight and other outside services) of $7.8 million, field supplies, testing supplies and equipment rental of $4.1 million, project-related travel expenses of $1.7 million and other direct costs of $1.5 million.
Selling, General and Administrative Expenses
Selling, general and administrative expenses consist of general corporate overhead, including executive, legal, finance, safety, risk management, human resource, marketing and information technology related costs, as well as indirect operational costs of labor, rent, insurance and stock-based compensation.
For the three months ended March 31, 2020, selling, general and administrative expenses were $20.9 million, an increase of $10.5 million or 100.4% versus the three months ended March 31, 2019, of which $1.9 million was from the existing selling, general and administrative expenses of companies we acquired after the first quarter 2019. The increase was also driven by an increased investment in corporate infrastructure (primarily finance, sales and marketing, safety, IT and human resources), an increase in bad debt expense, an increase in costs incurred related to acquisitions, and costs related to preparing for our initial public offering.
For the three months ended March 31, 2020, selling, general and administrative expenses were comprised of indirect labor of $5.9 million, facilities costs of $2.9 million, stock-based compensation of $0.7 million, bad debt expense of $6.3 million, and other costs (including software, travel, insurance, legal, consulting and audit services) of $5.1 million.
For the three months ended March 31, 2019, selling, general and administrative expenses were $10.4 million, which was comprised of indirect labor of $4.2 million, facilities costs of $2.5 million, stock-based compensation of $0.8 million, and other costs (including software, travel, insurance, legal, consulting and audit services) of $2.9 million.
We expect our general and administrative expenses to increase as a result of additional insurance, legal, accounting, investor relations and other costs associated with becoming a public company.
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