United Airlines and United Express operate approximately 4,800 flights a day to 353 airports across five continents. In 2018, United and United Express operated more than 1.7 million flights carrying more than 158 million customers. United is proud to have the world's most comprehensive route network including U.S. mainland hubs in Chicago, Denver, Houston, Los Angeles, Newark/New York, San Francisco and Washington, D.C. United operates 770 mainline aircraft and the airline's United Express carriers operate 559 regional aircraft. The airline is a founding member of Star Alliance, which provides service to 193 countries via 28 member airlines. For more information, visit united.com, follow @United on Twitter or connect on Facebook. The common stock of United's parent, United Continental Holdings Inc., is traded on the Nasdaq under the symbol "UAL".
The Company recorded net income of $1.1 billion in the second quarter of 2019 as compared to net income of $683 million in the second quarter of 2018. The Company considers a key measure of its performance to be operating income, which was $1.5 billion for the second quarter of 2019, as compared to $1.1 billion for the second quarter of 2018. Significant components of the Company's operating results for the three months ended June 30 are as follows (in millions, except percentage changes):
Operating Revenue. The table below shows year-over-year comparisons by type of operating revenue for the three months ended June 30 (in millions, except for percentage changes):
Passenger revenue increased $606 million, or 6.1%, in the second quarter of 2019 as compared to the year-ago period primarily due to a 5.1% increase in traffic. Second quarter PRASM increased 2.5% compared to the second quarter of 2018 primarily as a result of increased close-in demand in the domestic markets and overall demand improvements in the Atlantic and Latin markets.