Although demolition can often be the lowest-cost option, that, too, can be expensive and out of the reach of financially stressed airports. A good example is Oakland International Airport, which, at its peak in 2007, served 14.8 million passengers but served 9.3 million passengers last year.

In 2003, when United Airlines filed for bankruptcy, it walked away from a 25-year lease, signed in 1988, for the Oakland Maintenance Center. It consolidated its maintenance operations nearby at San Francisco International Airport.

According to Ms. Kramer’s report, the Port of Oakland has had trouble finding a replacement tenant that would generate comparable rental income. Nor does the port have the $4 million needed to demolish the building. The port uses the building for offices, and rents its exterior as billboard space, generating $200,000 in the fiscal year that ended in June.

While port officials declined to comment on their search for a new tenant for the maintenance building, they did say they have been able to increase general aviation operations on the north side of the airport. Michael A. Visconti, property manager on the north side of the airport for the Port of Oakland, said companies offering general aviation services paid the port rent and fees totaling $4.9 million in the past fiscal year.

Officials at Cincinnati/Northern Kentucky International Airport face many similar problems. Delta at one time operated a major hub there, flying 600 of the airport’s total of 650 daily departures in 2005.

Today, Delta is still the biggest carrier at the airport, but offers just 125 or so of the airport’s 170 daily departures. Delta occupies one concourse in the largest of the airport’s three terminals, and in May, the other carriers serving the airport — United, American Airlines, US Airways and Air Canada — all moved to the same terminal as Delta, leaving the other two terminals empty.

The airport is looking at its options, said Meghan Glynn, the airport’s vice president for external affairs, including demolishing one or both empty terminals and moving the rental car operation closer to the remaining terminal. Ms. Glynn said that if demolition took place, it would be financed by a combination of federal grants and passenger and customer facility charges.