Denver International Airport is not billing airlines accurately

Published on June 18, 2026

En español(PDF, 135KB)

DENVER - Weaknesses in Denver International Airport's airline billing processes resulted in both overbilling and in uncollected revenue, according to a new audit from Denver Auditor Timothy M. O'Brien, CPA. The audit also found the airport was not enforcing contract terms and its operations were not aligned with policies and procedures.

Our audit reviewed the airport's operating revenue from renting facilities to airlines and charging airlines landing fees, focusing on the two largest signatory airlines at the airport - Frontier Airlines and United Airlines.

"Right now, the airport is not ensuring it is collecting revenue from airlines promptly. I'm pleased the airport recognizes there's an issue, agreeing with all but one of our improvement recommendations," said Auditor O'Brien.

Billing issues

We found systemic issues with Denver International Airport's processes to calculate what it bills airlines to use certain airport gates. The airport overbilled United Airlines by about $5.94 million from January 2022 through September 2025. About $5.28 million, or 89%, of this total was incorrectly invoiced because airport staff charged United Airlines for using gates it already leased.

The airport overly relies on a year-end settlement process to correct billing errors not discovered during the year. But the year-end settlement process may not catch all errors from staff, like the $352,000 in credits we found the airport missed and owed to United for 2024.

"There's too much dependence on the year-end settlement to correct issues. The adjustments at the end of the year fall short of resolving issues. Improving processes during the year to ensure billing, credits, and invoicing are accurate will lead to a more efficient year-end settlement," said Auditor O'Brien.

Contract terms not enforced

There were about $1.6 million in interest penalties for late invoice payments the airport did not collect from Frontier Airlines and United Airlines from 2022 through 2024, despite clear contract terms about penalties.

We found Frontier and United had more than $13.7 million in outstanding and unapplied credits as of December 2025. Large outstanding credits complicate the airport's ability to charge interest against overdue payments from airlines.

The airport disagreed with our recommendation to reduce large, lingering credits.

Policies and procedures

The airport was also not following its own guidance for inspecting and billing spaces the airlines lease, monitoring gate use, and performing the year-end settlement process.

In a positive step, compared to our 2016 audit, airport staff are more quickly billing airlines that change the spaces they lease.

"Denver International Airport has proven it can adjust to more efficient processes. We will conduct a follow up audit to see whether the airport addresses the revenue issues we uncovered," Auditor O'Brien added.

AUDITOR TIMOTHY O'BRIEN, CPA
Denver Auditor

Denver Auditor's Office

201 W. Colfax Ave. #705 Denver, CO 80202
Email: [email protected]
Call: 720-913-5000
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