As global crude prices plunged earlier this month, Venezuela’s foreign minister asked to see Saudi Arabia’s top oil official at a climate-change conference on Margarita Island, off the South American coast.

Ali al-Naimi, the Saudi oil minister, was expecting a plea to reduce oil output and bolster markets. In anticipation, according to people familiar with the matter, he brought a message to Venezuelan Foreign Minister Rafael Ramirez: Saudi Arabia won’t cut production on its own.

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