We had one product tanker employed under time charter as at March 31, 2022 as compared with four as at March 31, 2021. Revenue days derived from time charters were 262 for the three months ended March 31, 2022, as compared to 169 for the three months ended March 31, 2021. The increase in revenue days for time-chartered vessels resulted in an increase in revenue of $1.7 million.
We had 2,126 spot revenue days for the three months ended March 31, 2022, as compared to 2,096 for the three months ended March 31, 2021. We had 26 and 22 vessels employed directly in the spot market as at March 31, 2022 and 2021, respectively. The increase in spot revenue days resulted in an increase in revenue of $0.6 million, while changes in spot rates resulted in an increase in revenue of $15.5 million for the three months ended March 31, 2022 as compared to the three months ended March 31, 2021. The Company managed three third party chemical tankers employed under spot as at March 31, 2022, compared with four as at March 31, 2021. This resulted in an increase in revenue of $0.1 million.
Voyage Expenses. Voyage expenses were $27.1 million for the three months ended March 31, 2022, an increase of $6.7 million from $20.4 million for the three months ended March 31, 2021. Voyage expenses increased primarily due to the increase in bunker prices resulting in an increase of $6.5 million and an increase in spot revenue days of $0.2 million for the three months ended March 31, 2022, as compared to the three months ended March 31, 2021.
TCE Rate. The average TCE rate for our fleet was $15,155 per day for the three months ended March 31, 2022, an increase of $3,806 per day from $11,349 per day for the three months ended March 31, 2021. The increase in average TCE rate was the result of higher spot rates for the three months ended March 31, 2022 as compared to the three months ended March 31, 2021. TCE rates represent net revenues (or revenue less voyage expenses) divided by revenue days, as further defined above.
Vessel Operating Expenses. Vessel operating expenses were $16.6 million for the three months ended March 31, 2022, an increase of $2.1 million from $14.5 million for the three months ended March 31, 2021. This increase is due to the timing of vessel operating expenses between quarters. Vessel operating expenses, by their nature, are prone to fluctuations between periods. Average fleet operating expenses per day, including technical management fees, were $6,921 per vessel for the three months ended March 31, 2022, as compared to $6,340 per vessel for the three months ended March 31, 2021. The timing of crew changes as a result of COVID-19 related delays in 2021 was a contributing factor in the difference for the three months ended March 31, 2022 when compared with March 31, 2021.
Charter Hire Costs. Charter hire costs were $2.1 million for the three months ended March 31, 2022, an increase of $0.9 million from $1.2 million from the three months ended March 31, 2021. We currently have two vessels chartered-in for the three months ended March 31, 2022 as compared to one vessel for the three months ended March 31, 2021.
Depreciation. Depreciation expense for the three months ended March 31, 2022, was $7.8 million, consistent with $7.8 million for the three months ended March 31, 2021.
Amortization of Deferred Drydock Expenditures. Amortization of deferred drydock expenditures for the three months ended March 31, 2022 was $1.2 million, a decrease of $0.3 million from $1.5 million for the three months ended March 31, 2021. The deferred costs of drydockings for a given vessel are amortized on a straight-line basis to the next scheduled drydocking of the vessel.
General and Administrative Expenses: Corporate. Corporate-related general and administrative expenses for the three months ended March 31, 2022 were $4.5 million, an increase of $0.3 million from $4.2 million for the three months ended March 31, 2021.
General and Administrative Expenses: Commercial and Chartering. Commercial and chartering expenses are the expenses attributable to our chartering and commercial operations departments in connection with our spot trading activities. Commercial and chartering expenses for the three months ended March 31, 2022 were $0.9 million, an increase of $0.1 million from $0.8 million for the three months ended March 31, 2021.