anticipate seismic data acquisition activity in the lower 48 to reach a low in the second quarter and into the third quarter of 2021 with slight improvement later in 2021.
During the latter part of 2018 and continuing into the first half of 2020, we successfully acquired multiple high density, large channel count projects in certain areas of the Permian Basin. These fully processed data sets first became available to the industry in late 2019 and continue into 2021. Early results of these data sets indicate substantially improved subsurface image quality compared to prior seismic data sets, examples of which are just beginning to become public. The increases in data quality and imagery are currently being utilized for improved well planning, geo-steering of long lateral well bores, geo-hazard identification and avoidance, enhanced reservoir definition and rock property description between well data samples and strategic placement of disposal well locations. As the industry begins to recognize and appreciate the value of these high density, large channel count surveys, we believe demand for such surveys will improve. Our state-of-the-art equipment base allows us to deploy multiple large channel count crews when demand does improve.
In our continuing response to these difficult times, we significantly limited capital budget spending, reduced fixed and variable operating expenses, and implemented a comprehensive equipment maintenance program in preparation for a rapid response to increased activity levels. We continue to maintain our commitment to our robust Health, Safety and Environmental program, ongoing relationships, and product quality.
While our revenues are mainly affected by the level of client demand for our services, our revenues are also affected by the pricing for our services that we negotiate with our clients and the productivity and utilization level of our data acquisition crews. Factors impacting productivity and utilization levels include: client demand, commodity prices, whether we enter into turnkey or dayrate contracts with our clients, the number and size of crews, the number of recording channels per crew, crew downtime related to inclement weather, delays in acquiring land access permits, agricultural or hunting activity, holiday schedules, short winter days, crew repositioning and equipment failure. To the extent we experience these factors, our operating results may be affected from quarter to quarter. Consequently, our efforts to negotiate more favorable contract terms in our supplemental service agreements, mitigate permit access delays and improve overall crew productivity may contribute to growth in our revenues. Further, the ongoing COVID-19 pandemic may further compound one or more of the foregoing factors and could directly affect our productivity.
Results of Operations
Operating Revenues. Operating revenues for the first quarter of 2021 decreased 69.9% to $11,748,000 compared to $38,979,000 in the same period of 2020. The decreased revenue during the first quarter of 2021 compared to the first quarter of 2020 was primarily due to low crew utilization during those periods of 2021.
Operating Expenses. Operating expenses for the first quarter of 2021 decreased 62.3% to $10,942,000 compared to $29,016,000 in the same period of 2020. The decrease in operating expenses was primarily due to decreased crew utilization during the first quarter of 2021 compared to the same period of 2020.
General and Administrative Expenses. General and administrative expenses were 23.9% and 9.4% of revenues in the first quarter of 2021 and 2020, respectively. General and administrative expenses decreased $867,000 or 23.6% to $2,807,000 during the first quarter of 2021 from $3,674,000 during the same period of 2020. The primary factors for the decrease in general and administrative expenses during the first quarter of 2021 compared to the same period of 2020 was due to workforce reductions, salary reductions, and continued cost reduction efforts by management.
Depreciation and Amortization Expense. Depreciation and amortization expense for the first quarter of 2021 totaled $3,434,000 compared to $4,904,000 for the same period of 2020. Depreciation expense decreased in 2021 compared to 2020 as a result of multiple years of reduced capital expenditures. Our depreciation expense is expected to remain below that of 2020 for the remainder of 2021 due to the anticipated continuation of maintenance levels of capital expenditures to maintain our existing asset base.
Total operating costs for the first quarter of 2021 were $17,183,000, representing a 54.3% decrease from the same period of 2020. This decrease was primarily due to the factors described above.
Income Taxes. There was no income tax benefit or expense for the first quarter 2021, compared to an income tax benefit of $1,000 for the same period of 2020. These amounts represent effective tax rates of 0.0% and -0.2%, respectively. The Company’s effective tax rate increased compared to the corresponding period from the prior year primarily due to 2020’s profitability in the quarter compared to a loss for the year.
Our effective tax rates differ from the statutory federal rate of 21.0% for certain items such as state and local taxes, valuation allowances, non-deductible expenses and discrete items. For further information, see Note 9 of the Notes to the Condensed Consolidated Financial Statements.