Pursuant to a congressional request, GAO examined issues regarding the new Denver airport, focusing on whether: (1) the new airport is more prone to adverse weather than the current airport, resulting in greater flight safety hazards; (2) adequate design and construction methods are being used to protect airport runways and other structures from soils that expand when wet; (3) the new airport would reduce air traffic delays at Denver or system-wide; and (4) the project is financially viable, given current budget costs and revenue projections. GAO found: (1) adverse weather conditions do not occur more often or in greater severity at the new airport site and pose no added flight safety hazards; (2) expansive soils like those at the new airport site are common throughout the Denver region and can lead to premature replacement or high maintenance costs for structures built on them, but design engineers have included proven methods for controlling and minimizing soil expansion and Denver implemented a quality assurance program to monitor construction at the site; (3) the new airport has design advantages over the current airport that should reduce local air traffic delays, but reductions in system-wide delays are unclear; (4) the new airport will cost nearly $4 billion, including costs for land, design, construction, and financing; (5) most of these costs will be financed through revenue bonds which paid off using the revenues of the airport; (6) to repay those bonds successfully, Denver must control its costs so as to minimize the amount of money it must borrow and generate enough revenues to pay the costs both of operating and maintaining the airport and of meeting the debt service on the bonds; and (7) cost overruns, schedule slippages, the loss of a hub carrier, and traffic shortfalls could increase the possibility of default.