How Denver International Airport became one of the fastest-growing airports in the world

Last year was Denver International Airport's busiest on record.

While airline stocks have yet to fully recover to pre-pandemic levels, passengers have returned in droves — and millions of them are flying through the Colorado hub.

"We will end 2023 much higher than our forecast at about 78 million passengers annually," said Phil Washington, CEO of the Denver International Airport. "So this has been tremendous growth."

The airport, known as DIA to Colorado locals, opened in 1995. It was originally built to handle 50 million passengers per year, but now that number is expected to reach more than 100 million people per year by 2027, according to DIA estimates.

OAG, a global travel data provider, said Denver went from the 21st busiest airport in the world in 2019 to the sixth in 2023. 

United Airlines is Denver's biggest operator with 46.7% market share, followed by Southwest at 30.7% and Frontier Airlines at 9.7%, according to DIA.

The midcontinent airport has become United's busiest hub. It recently invested nearly $1 billion in Denver to add more gates, flights and destinations, and opened the largest lounge in its network.

"About 60% of our customers are connecting from other places. Forty percent of our customers are local Denver, and it's a fast growing city," said Jonna McGrath, vice president of Denver Airport operations for United Airlines. "We want to grow before 2030 to about 650 flights a day."

CNBC got a behind-the-scenes look at United's Denver operations and explored how the airport and the airline plan to keep up with demand.

Watch the video to learn more.