As stock prices fell today, so did the price of oil. The price of crude has dropped 30 percent since last month amid signs the world economy and oil demand are slowing down. And there’s plenty of oil about. Even so, you might want to fill up your tank now and be worried. Influential voices in the oil market are warning that oil-producing states may not be able to produce much more oil; that the market in the longer term could swing from having too much to having too little.

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