The Justice Department said Continental and United were already planning to sell seats on each other's U.S. flights, combine customer lounges, consolidate operations at airports served by both and work together on procurement. The Justice Department said such an arrangement could closely resemble a merger of Chicago-based United, the No. 3 U.S. carrier, and Houston-based Continental, the fourth-largest, and lead to higher fares.

Continental plans to switch from SkyTeam to the Star Alliance in October. Continental expects to play a stronger role in service to Latin America and elsewhere as part of Star instead of competing within its own team by sharing many overlapping routes with Delta. Continental didn't have antitrust immunity in SkyTeam.

The antitrust immunity for Continental will extend to its cooperation with other Star Alliance members Austrian Airlines, bmi, LOT Polish Airlines, Scandinavian Airlines, Swiss and TAP Air Portugal.

Friday's decision could also boost AMR Corp.'s American Airlines, which is seeking antitrust immunity to work with British Airways and Spain's Iberia on trans-Atlantic service.

Shares of Continental rose 61 cents, or 6.5 percent, to close at $10; United parent UAL Corp. gained 8 cents, or 2.5 percent, to finish at $3.26; and AMR added 19 cents, or 4.8 percent, to end at $4.17.