LONDON—The escalating duel surrounding U.S. and OPEC oil production has ensnared Nigeria’s energy sector, highlighting a challenge for the petroleum cartel ahead of its meeting Friday.

The West African nation, a member of the Organization of the Petroleum Exporting Countries, has lost business in its main market in the U.S. and struggled to gain footholds elsewhere, raising a question for OPEC on whether its decision to fight for market share may have left behind more-vulnerable members.

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