awarded several additional mid-sized projects in the lower 48, each of which will be pushed into late 2022 primarily due to land access issues. Bid activity remains at historically low levels and visibility into 2022 is limited in the lower 48. Due to a lack of demand for seismic data acquisition projects in both Canada and the lower 48, prices for our services softened in the last quarter.
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 anticipated increased activity levels. In addition, we maintain our commitment to our robust Health, Safety and Environmental program, ongoing client 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 third quarter of 2021 decreased 78.1% to $1,914,000 compared to $8,738,000 in the same period of 2020. Operating revenues decreased 82.1% to $13,855,000 during the first nine months of 2021 compared to $77,216,000 in the same period of 2020. The decreased revenue during the third quarter and first nine months of 2021 compared to the same periods of 2020 was primarily due to lower demand and extended periods of low utilization during those periods of 2021.
Operating Expenses. Operating expenses for the third quarter of 2021 decreased 57.9% to $3,975,000 compared to $9,441,000 in the same period of 2020. Operating expenses decreased 68.6% to $18,247,000 during the first nine months of 2021 compared to $58,189,000 in the same period of 2020. The decrease in operating expenses during the third quarter and first nine months of 2021 compared to the same periods of 2020 was primarily due to decreased crew utilization during those periods of 2021.
General and Administrative Expenses. General and administrative expenses were 127.6% and 57.7% of revenues in the third quarter and first nine months of 2021, respectively compared to 37.4% and 14.5% of revenues in the same periods of 2020. General and administrative expenses decreased $827,000 or 25.3% to $2,443,000 during the third quarter of 2021 from $3,270,000 during the same period of 2020, and decreased $3,209,000 or 28.6% to $7,996,000 during the first nine months of 2021 from $11,205,000 during the same period of 2020.The primary factors for the decrease in general and administrative expenses during the third quarter and first nine months of 2021 compared to the same periods 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 third quarter and first nine months of 2021 totaled $3,249,000 and $10,083,000, respectively, compared to $4,125,000 and $13,412,000 for the same periods 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 third quarter of 2021 were $9,667,000, representing a 42.6% decrease from the same period of 2020. The operating costs for the first nine months of 2021 were $36,326,000, representing a 56.1% decrease from the same period of 2020. The decrease in operating costs for the third quarter and first nine months of 2021 compared to 2020 was primarily due to the factors described above.
Income Taxes. Income tax expense for the third quarter and first nine months of 2021 was $0 and $0, respectively, compared to income tax expense of $15,000 and $15,000 for the same periods of 2020. These amounts represent effective tax rates of 0.0% and 0.0% for the third quarter and first nine months of 2021, respectively, compared to -0.2% and -0.3% for the third quarter and first nine months of 2020. The Company’s nominal or no effective tax rate for the periods above was due to the presence of net operating loss carryovers and adjustments to the valuation allowance on deferred tax assets.
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.