Oil, natural gas and natural gas liquids revenues were $80.5 million and $39.4 million for the three months ended September 30, 2021 and 2020, respectively. The increase in revenues is primarily attributable to an approximate $24.25 per Boe increase in our average realized prices (excluding the effects of hedging arrangements). The amount we realize for our production depends predominantly upon commodity prices, which are affected by changes in market demand and supply, as impacted by overall economic activity, weather, transportation take-away capacity constraints, inventory storage levels, quality of production, basis differentials and other factors. For the three months ended September 30, 2021 and 2020, production averaged 17,728 Boe/d and 17,076 Boe/d, respectively. Our average daily production increased in the three months ended September 30, 2021 when compared to the same period in the prior year due to new production brought online as a result of our 2021 capital program.
Lease operating expenses were $12.0 million and $10.1 million for the three months ended September 30, 2021 and 2020, respectively. On a per unit basis, lease operating expenses were $7.34 per Boe and $6.42 per Boe for the three months ended September 30, 2021 and 2020, respectively. The increase in lease operating expenses in 2021 results from a market increase in maintenance, power, and chemical costs.
Workover and other expenses were $1.0 million and $0.9 million for the three months ended September 30, 2021 and 2020, respectively. On a per unit basis, workover and other expenses were $0.61 per Boe and $0.58 per Boe for the three months ended September 30, 2021 and 2020, respectively. The increased workover and other expenses in 2021 relate to more significant workover projects undertaken in the current year.
Taxes other than income were $3.1 million and $2.7 million for the three months ended September 30, 2021 and 2020, respectively. Most production taxes are based on realized prices at the wellhead. As revenues or volumes from oil and natural gas sales increase or decrease, production taxes on these sales also increase or decrease. On a per unit basis, taxes other than income were $1.89 per Boe and $1.73 per Boe for the three months ended September 30, 2021 and 2020, respectively.
Gathering and other expenses were $15.9 million and $13.5 million for the three months ended September 30, 2021 and 2020, respectively. Gathering and other expenses include gathering fees paid to third parties on our oil and natural gas production and operating expenses of our gathering support infrastructure. Approximately $6.3 million and $3.8 million for the three months ended September 30, 2021 and 2020, respectively, relate to gathering and marketing fees paid to third parties on our oil and natural gas production. Gathering and marketing fees increased in 2021 as we marketed higher quantities of sour gas production to third parties in the current year period. Approximately $9.6 million and $9.7 million for the three months ended September 30, 2021 and 2020, respectively, relate to operating expenses on our treating equipment and gathering support facilities. The decrease in treating equipment and gathering support facilities expenses in 2021 results from lower operating expenses associated with our treating equipment, as fewer sour gas production volumes were processed through our hydrogen sulfide treating plant in the current year period, which were partially offset by higher chemical costs to improve the quality of treated oil.
General and administrative expense was $4.0 million and $3.5 million for the three months ended September 30, 2021 and 2020, respectively. The increase in general and administrative expense in the current year period is associated with an increase in payroll and professional fee costs partially offset by a decrease in information technology expenses incurred and the Employee Retention Credit. On a per unit basis, general and administrative expenses were $2.46 per Boe and $2.22 per Boe for the three months ended September 30, 2021 and 2020, respectively.
Depletion for oil and natural gas properties is calculated using the unit of production method, which depletes the capitalized costs of evaluated properties plus future development costs based on the ratio of production for the current period to total reserve volumes of evaluated properties as of the beginning of the period. Depletion expense was $10.7 million and $15.3 million for the three months ended September 30, 2021 and 2020, respectively. On a per unit basis, depletion expense was $6.57 per Boe and $9.76 per Boe for the three months ended September 30, 2021 and 2020, respectively. The lower depletion rate in the 2021 is attributable to the change in our depletable base as a result of full cost ceiling test impairments incurred in 2020.
Under the full cost method of accounting, we are required on a quarterly basis to determine whether the book value of our oil and natural gas properties (excluding unevaluated properties) is less than or equal to the “ceiling”, based upon the expected after tax present value (discounted at 10%) of the future net cash flows from our proved reserves. Any