Other revenue
Other revenue consists of the amortization of contract liabilities related to capital reimbursements received from our customers. Other revenue for the year ended December 31, 2021, increased by $1.7 million, or 85.7%, to $3.7 million, compared to $2.0 million for the year ended December 31, 2020, primarily due to new capital reimbursements received resulting in increased amortization. Other revenues are included entirely in the Gathering and Processing segment.
Cost of sales (exclusive of depreciation and amortization)
Cost of sales (exclusive of depreciation and amortization) primarily consists of purchases of NGLs and natural gas from our producers at contracted market prices to support product sales to other third parties. Cost of sales for the year ended December 31, 2021, increased $168.5 million or 259.1%, to $233.6 million, compared to $65.1 million for the year ended December 31, 2020, primarily due to the period over period increase in commodity prices. Cost of sales (exclusive of depreciation and amortization) are included entirely in the Gathering and Processing segment.
Depreciation and amortization
Depreciation and amortization consists of depreciation expense on property, plant and equipment and amortization expense for intangible assets. Depreciation and amortization for the year ended December 31, 2021, increased $19.8 million, or 8.8%, to $243.6 million, compared to $223.8 million for the year ended December 31, 2020, primarily due to an increase in our depreciable asset base from projects placed into service over the past year.
Operating expenses
Operating expenses consist of equipment rental fees, labor, outside services, and lubricants and chemicals all incurred in the operation of our assets. Operating expenses for the year ended December 31, 2021, decreased $2.8 million, or 3.0%, to $90.9 million, compared to $93.7 million for the year ended December 31, 2020, primarily due to decreased electricity costs associated with electricity credits received from one of our primary electricity providers during the month of February.
General and administrative expenses
General and administrative expenses consist of day-to-day costs we incur to administer our business including administrative labor, insurance costs and legal fees. General and administrative expenses for the year ended December 31, 2021, increased $5.7 million, or 24.7%, to $28.6 million, compared to $22.9 million for the year ended December 31, 2020, primarily due to $5.7 million of transactions costs incurred for the Altus merger during the current year.
Ad valorem taxes
Ad valorem taxes for the year ended December 31, 2021, increased $0.5 million, or 4.8%, to $11.5 million, compared to $11.0 million for the year ended December 31, 2020, primarily due to the aforementioned increase to our fixed asset base and its increased utilization.
Loss on disposal of assets
Loss on disposal of assets consists of the losses associated with the dispositions of fixed assets. Loss on disposal of assets for the year ended December 31, 2021, decreased $3.1 million, or 88.9%, to $0.4 million, compared to $3.5 million for the year ended December 31, 2020, primarily due to the write-off of a compressor during the year ended December 31, 2020.
Goodwill impairment
Goodwill impairment represents the charge to earnings and is calculated as the amount by which a reporting unit’s carrying value exceeds its fair value, determined during a goodwill impairment test. Goodwill impairment decreased $1.0 billion due to the goodwill impairment for the year ended December 31, 2020 and no impairment taken during the year ended December 31, 2021.
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