I quote from Page No. 88 of Annual reports of Reliance Industries Ltd. in Directors Report -
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Exceptional item of Rs.4733 crore ($1.2 billion) represents gains primarily arising out of transactions concerning shares of Reliance Petroleum Ltd., a subsidiary of the Company.
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Now it is clear that Reliance Petroleum is a subsidiary of Reliance Industries Ltd. since it is mentioned in the Balance Sheet of the company itself.