Impairment of Oil, Natural Gas and Natural Gas Liquids Expense
We recorded an impairment expense on our oil and natural gas properties of $22.2 million and $34.9 million during the three months ended September 30, 2020 and 2019, respectively. The impairment recorded during the three months ended September 30, 2020 was due to the recent significant decline in the trailing twelve month average of oil and natural gas prices, related to reduced demand for oil and natural gas as a result of COVID-19, the announcement of price reductions and production increases in March 2020 by members of OPEC and other foreign, oil-exporting countries, and other supply factors. The impairment recorded for the three months ended September 30, 2019 was primarily a result of a decline in the 12-month average price of oil and natural gas.
Marketing and Other Deductions
Our marketing and other deductions include product marketing expense, which is a post-production expense. Marketing and other deductions for the three months ended September 30, 2020 were $2.5 million, an increase of $0.2 million from $2.3 million for the three months ended September 30, 2019, which was attributable to the Springbok Acquisition.
General and Administrative Expenses
General and administrative expenses for the three months ended September 30, 2020 were $6.1 million, an increase of $0.4 million from $5.7 million for the three months ended September 30, 2019. Included within general and administrative expenses are non-cash expenses for unit-based compensation as a result of the amortization of restricted units that have been issued by us over various periods. The increase in general and administrative expenses was primarily attributable to a $0.6 million increase in unit-based compensation expense, which was partially offset by a $0.2 million decrease in cash general and administrative expenses.
Interest Expense
Interest expense for the three months ended September 30, 2020 was $1.6 million compared to $1.5 million for the three months ended September 30, 2019. The increase in interest expense was primarily due to debt incurred to fund the Springbok Acquisition. The increase in interest expense was partially offset by the repayment of $2.5 million in debt during the three months ended September 30, 2020 and the decline in the weighted average interest rate from 4.57% during the three months ended September 30, 2019 to 2.92% during the three months ended September 30, 2020.
Comparison of the Nine Months Ended September 30, 2020 to the Nine Months Ended September 30, 2019
Oil, Natural Gas and NGL Revenues
For the nine months ended September 30, 2020, our oil, natural gas and NGL revenues were $66.7 million, a decrease of $13.6 million from $80.3 million for the nine months ended September 30, 2019. The significant decrease in oil, natural gas and NGL revenues was directly related to the decrease in the average prices we received for oil, natural gas and NGL production for the nine months ended September 30, 2020 as discussed below. This decrease was partially offset by an increase in production associated with various acquisitions throughout the 2019 and 2020 periods.
Our revenues are a function of oil, natural gas, and NGL production volumes sold and average prices received for those volumes. The production volumes were 3,778,891 Boe or 13,792 Boe/d, for the nine months ended September 30, 2020, an increase of 436,500 Boe or 1,549 Boe/d, from 3,342,391 Boe or 12,243 Boe/d, for the nine months ended September 30, 2019. The increase in production for the nine months ended September 30, 2020 was primarily attributable to production associated with the Springbok Acquisition, which accounted for 375,535 Boe or 2,249 Boe/d. Our production for the nine months ended September 30, 2019 included a non-routine increase in production related to the recognition of unknown upside production associated with the assets acquired in the Haymaker Acquisition, which accounted for 188,882 Boe or 2,053 Boe/d.
Our operators received an average of $36.08 per Bbl of oil, $1.70 per Mcf of natural gas and $11.47 per Bbl of NGL for the volumes sold during the nine months ended September 30, 2020 compared to $54.65 per Bbl of oil, $2.33 per Mcf of natural gas and $16.83 per Bbl of NGL for the volumes sold during the nine months ended September 30, 2019.