The U.S. Department of Transportation gave final approval Thursday to an expanded transatlantic alliance involving Delta and Northwest Airlines.

The two U.S. carriers and four of their international partners can coordinate their fares, services and capacity as if they were a single carrier in the transatlantic market with antitrust immunity, subject to certain conditions. The action includes Air France, Alitalia, Czech Airlines and KLM Royal Dutch Airlines. It is independent of the Justice Department's review of a pending merger between Delta and Northwest.

DOT said the proposed alliance is in the public interest because it will likely produce efficiencies and new options for price and service. The U.S.-EU open skies agreement provides that transatlantic markets remain open to other competitors because U.S. and European airlines are now able to serve any route between the United States and Europe.

The carriers have not yet created a working joint venture that will provide the public benefits foreseen. So, DOT required the carriers to fully implement the proposed alliance within 18 months as a condition of retaining antitrust immunity. The carriers will remain subject to antitrust laws for domestic service and international flights that are not covered by the agreement.