JetBlue Airways is buying Spirit Airlines for $3.8 billion in a deal that could increase competition at the top end of the U.S. airline industry while eliminating the largest discount airline for travelers on a tight budget.

The agreement announced Thursday capped bidding war that began in April, and it came one day after Spirit’s attempt to merge with rival discount carrier Frontier Airlines fell apart.

JetBlue and Spirit would become the fifth-largest U.S. carrier, with about 9% of the market. The combined airline would move much closer to the leaders — American, United, Delta and Southwest — while leaving the rest of the pack far behind.

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“Spirit is going to disappear, and with it, its low-cost structure,” said William McGee of the anti-merger American Economic Liberties Project. “There is no question that fares are going to go up.”

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