PARIS — TotalFina of France successfully concluded a bid to acquire Elf Aquitaine in an agreement that would create the world’s fourth-largest oil company. But the European Commission said the proposed deal could reduce competition and indicated that the merger would require extensive review and revisions.

The $54.2-billion deal is the latest in a series of mergers that have reshaped the oil industry, including the combination of British Petroleum and Amoco Corp. and the pending deal that will unite Exxon Corp. and Mobil Corp.

Elf Aquitane initially resisted the takeover by TotalFina, but later agreed to a friendly merger.