As of September 30, 2021, approximately 45.5% of our aircraft in scheduled service or under contract were operated for United, approximately 29.8% were operated for Delta, approximately 18.1% were operated for American and approximately 6.6% were operated for Alaska.
Historically, multiple contractual relationships with major airlines have enabled us to reduce our reliance on any single major airline code and to enhance and stabilize operating results through a mix of fixed-fee arrangements (referred to as “capacity purchase agreements”) and revenue-sharing arrangements (referred to as “prorate” agreements). For the nine months ended September 30, 2021, capacity purchase revenue and prorate revenue represented approximately 83.9% and 16.1%, respectively, of our total flying agreements revenue. On contract routes, the major airline partner controls scheduling, ticketing, pricing and seat inventories and we are compensated by the major airline partner at contracted rates based on completed block hours (measured from takeoff to landing, including taxi time), flight departures, the number of aircraft under contract and other operating measures. On prorate routes, we have more control over scheduling, pricing and seat inventories, and we share passenger fares with our major airline partners according to prorate formulas. Our prorate revenue and profitability may fluctuate based on ticket prices and passenger loads, and we are responsible for the operating costs of the prorate flights, including fuel and airport costs.
Third Quarter Summary
We had total operating revenues of $744.8 million for the three months ended September 30, 2021, a 62.8% increase compared to total operating revenues of $457.5 million for the three months ended September 30, 2020. We had net income of $9.7 million, or $0.19 per diluted share, for the three months ended September 30, 2021, compared to net income of $33.7 million, or $0.66 per diluted share, for the three months ended September 30, 2020. The significant items affecting our revenue and operating expenses during the three months ended September 30, 2021, are outlined below:
Revenue
The number of aircraft we have in scheduled service and the number of block hours we incur on our flights are primary drivers to our flying agreements revenue under our capacity purchase agreements. The number of flights we operate and the corresponding number of passengers we carry are the primary drivers of our revenue under our prorate flying agreements. As a result of higher passenger demand compared to the onset of the COVID-19 pandemic, the number of aircraft we operated increased from 448 as of September 30, 2020, to 486 as of September 30, 2021; the number of block hours increased from 222,561 for the three months ended September 30, 2020, to 370,462 for the three months ended September 30, 2021, or by 66.5%; and the number of passengers we carried increased from 4.9 million for the three months ended September 30, 2020, to 10.9 million, or by 120.9%.
As a result of increased flight schedules and additional aircraft operating under our capacity purchase agreements for the three months ended September 30, 2021, as compared to three months ended September 30, 2020, our capacity purchase revenue increased $206.5 million, or 53.7%. Additionally, we recognized $19.2 million of previously deferred revenue during the three months ended September 30, 2021, compared to deferring revenue of $29.6 million of fixed monthly payments received under our capacity purchase agreements for the three months ended September 30, 2020, as further described in the section of this report entitled “Results of Operations.” As a result of increased flight schedules and passengers carried on our prorate routes, our prorate revenue increased $67.5 million, or 111.1% for the three months ended September 30, 2021, as compared to the three months ended September 30, 2020.
Operating Expenses
Our total operating expenses increased $314.8 million, or 82.2% for the three months ended September 30, 2021, compared to the three months ended September 30, 2020. This increase was primarily due to an increase in the number of flights we operated and a non-cash impairment charge of $84.6 million for the three months ended September 30, 2021. Departures increased from 137,493 for the three months ended September 30, 2020, to 210,251 for the three months ended September 30, 2021, or by 52.9%. During the three months ended September 30, 2021, we recorded a non-cash impairment charge of $84.6 million to write-down CRJ900 aircraft operating under Delta capacity purchase agreements to their estimated fair value. Additional details regarding the increase in our operating expenses are described in the section of this Report entitled “Results of Operations.”