major airline partner, or if purchased by us, we record the direct reimbursement as a reduction to our fuel expense. The following table summarizes the gallons of fuel we purchased under our prorate agreements, for the periods indicated:
| | | | | | | | | |
| | For the six months ended June 30, |
(in thousands) | | 2023 | | 2022 | | % Change |
Fuel gallons purchased | | | 10,766 | | | 14,196 | | (24.2) | % |
Fuel expense | | $ | 39,243 | | $ | 56,910 | | (31.0) | % |
Airport-related expenses. Airport-related expenses include airport-related customer service costs such as outsourced airport gate and ramp agent services, airport security fees, passenger interruption costs, deicing, landing fees and station rents. The $1.4 million, or 3.9%, decrease in airport-related expenses for the six months ended June 30, 2023, compared to the six months ended June 30, 2022, was primarily due to a decrease in subcontracted airport services and landing fees as a result of a decrease in the number of flights we operated under our prorate arrangements.
Aircraft rentals. The $10.1 million, or 31.4%, decrease in aircraft rentals was primarily related to a decrease in our leased aircraft since the six months ended June 30, 2022. In March 2023, we acquired 24 CRJ700 aircraft and eight CRJ200 aircraft under an early lease buyout for $125.5 million, of which $86.9 million was capitalized as fixed assets and $38.6 million was applied towards previously recorded lease liabilities.
Other operating expenses. Other operating expenses primarily consist of property taxes, hull and liability insurance, simulator costs, crew per diem and crew hotel costs. The $15.9 million, or 10.2%, decrease was primarily related to a decrease in other operating costs as a result of the lower number of flights we operated during the six months ended June 30, 2023, compared to the six months ended June 30, 2022, such as crew per diem and crew hotel costs.
Summary of interest expense, interest income, other income, net and provision for income taxes
Interest Expense. The $8.3 million, or 14.1%, increase in interest expense was primarily related to higher interest rates on debt issued since June 30, 2022.
Interest income. Interest income increased $17.5 million, from $3.0 million for the six months ended June 30, 2022, to $20.5 million for the six months ended June 30, 2023. The increase in interest income was primarily related to an increase in our average investment in marketable securities for the three and six months ended June 30, 2023, compared to the three and six months ended June 30, 2022, and an increase in average interest rates attributed to our marketable securities for the same comparable periods.
Other income, net. Other income, net decreased $1.7 million during the six months ended June 30, 2023, compared to the six months ended June 30, 2022. Other income, net primarily consists of the unrealized gains on our investments in other companies, income related to our investment in a joint venture with a third party and gains or losses on the sale of assets. The decrease in other income, net was primarily a result of a decrease in unrealized gains on our investments in other companies for the six months ended June 30, 2023, compared to the six months ended June 30, 2022.
Provision (benefit) for income taxes. For the six months ended June 30, 2023 and 2022, our effective income tax rates were 21.6% and 26.5%, respectively, which included the statutory federal income tax rate of 21% and other reconciling income tax items, including state income taxes, the impact of non-deductible expenses and a discrete tax expense on employee equity transactions. The decrease in the effective tax rate primarily related to pre-tax loss for the six months ended June 30, 2023, compared to pre-tax income for the six months ended June 30, 2022 and the impact of increases in non-deductible expenses for the six months ended June 30, 2023, compared the six months ended June 30, 2022.
Net income (loss). Primarily due to the factors described above, we generated a net loss of $6.7 million, or $0.14 loss per share, for the six months ended June 30, 2023, compared to net income of $71.7 million, or $1.42 per diluted share, for the six months ended June 30, 2022.