United shares are up about 75% this year. The market likes the merger with Continental, which was announced in May, not to mention the speedy approval that came less than four months later.

Analysts are split on whether United can quickly capitalize on the merger. Standard & Poor's analyst Jim Corridore has a buy on the shares and a $34 price target. The merger "will give the combined carrier an improved international route map with the potential for cost and revenue synergies," he wrote, in a recent report. He also thinks the industry's biggest market share will enable a RASM premium.

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