expense decreased from $0.67 per Mcfe for the three months ended June 30, 2020 to $0.62 per Mcfe for the three months ended June 30, 2021, primarily as a result of increased proved reserve volumes between periods.
General and administrative expense. General and administrative expense (excluding equity-based compensation expense) decreased from $30 million for the three months ended June 30, 2020 to $28 million for the three months ended June 30, 2021, a decrease of $2 million, or 8%. The decrease was primarily due to lower employee headcount during 2021. We had 524 and 504 employees as of June 30, 2020 and 2021, respectively. On a per-unit basis, general and administrative expense excluding equity-based compensation was $0.09 per Mcfe for both the three months ended June 30, 2020 and 2021, respectively.
Equity-based compensation expense. Noncash equity-based compensation expense decreased from $8 million for the three months ended June 30, 2020 to $4 million for the three months ended June 30, 2021, primarily due to equity award forfeitures partially offset by new awards granted to employees. When an equity award is forfeited, expense previously recognized for the award is reversed. Please see Note 9—Equity Based Compensation and Cash Awards to the unaudited condensed consolidated financial statements for more information on equity-based compensation awards.
Marketing Segment
Marketing. Where feasible, we purchase and sell third-party natural gas and NGLs and market our excess firm transportation capacity, or engage third parties to conduct these activities on our behalf, to optimize the revenues from these transportation agreements. We have entered into long-term firm transportation agreements for a significant portion of our current and expected future production to secure guaranteed capacity to favorable markets.
Net marketing expenses decreased from $49 million, or $0.15 per Mcfe, for the three months ended June 30, 2020 to $34 million, or $0.11 per Mcfe, for the three months ended June 30, 2021. The decrease in net marketing expense was driven by higher marketing volumes and margins that mitigated some of our excess firm transportation expense.
Marketing revenues increased from $64 million for the three months ended June 30, 2020 to $165 million for the three months ended June 30, 2021, an increase of $101 million.
Marketing expenses increased from $113 million for the three months ended June 30, 2020 to $199 million for the three months ended June 30, 2021, an increase of $86 million, or 76%. Marketing expenses include firm transportation costs related to current excess firm capacity as well as the cost of third-party purchased gas and NGLs. Firm transportation costs included in the expenses above were $41 million and $19 million for the three months ended June 30, 2020 and 2021, respectively.
Equity Method Investment in Antero Midstream Corporation
Antero Midstream Corporation. Revenue from the Antero Midstream Corporation segment increased from $220 million for the three months ended June 30, 2020 to $233 million for the three months ended June 30, 2021, an increase of $13 million, or 6%, primarily due to higher gathering and compression revenues as a result of increased throughput between periods, partially offset by lower water handling revenue as a result of operational efficiencies. Total operating expenses related to the segment decreased from $85 million for the three months ended June 30, 2020 to $81 million for the three months ended June 30, 2021, primarily due to lower water handling operating expenses as a result of operational efficiencies, partially offset by increased gathering and compression expenses due to higher throughput volumes.
Items Not Allocated to Segments
Interest expense. Our interest expense decreased from $52 million for the three months ended June 30, 2020 to $50 million for the three months ended June 30, 2021, a decrease of $2 million or 4%, primarily due to the reduction in debt as a result of the repurchase of certain our unsecured senior notes and increased interest income between periods, partially offset by interest that accrued on the 2026 Convertible Notes, 2026 Notes, 2029 Notes and 2030 Notes, each of which was issued after June 30, 2020.
Gain (loss) on early extinguishment of debt. During the three months ended June 30, 2020, we recognized a gain on early extinguishment of debt of $39 million related to $236 million principal amount of debt that we repurchased at a weighted average discount of 17%. During the three months ended June 30, 2021, we equitized $56 million aggregate principal amount of our 2026 Convertible Notes in the May Equitization Transactions and as a result, we recognized a loss of $21 million which represents the difference between the fair value of the liability component of the 2026 Convertible Notes and the carrying value of such notes. Additionally, during the three months ended June 30, 2021, we redeemed the remaining balance of $574 million of our 2023 Notes at