The report by the Press Trust of India putting his wealth at 63.
2 billion dollars saw newspapers hailing his rise as another triumph for the nation's booming economy.
But Reliance said Ambani was not quite so rich after all, with a net worth of somewhere in the region of 50 billion dollars.
The multi-billionaire was listed by Forbes magazine earlier this year in 14th place among the world's richest people with an estimated wealth of 20.
1 billion dollars, way behind Microsoft's Bill Gates on 56 billion dollars.
According to PTI, the breakneck rise in India's benchmark Sensex index -- which rocketed to 20,000 points Monday, after gaining nearly 4,000 points in six weeks -- meant 49-year-old Ambani was now worth 63.2 billion.
"They are completely wrong. They have done double calculations," Reliance spokesman Tushar Pania told AFP, explaining that Ambani, 49, does not have a direct share in Reliance Petroleum.
PTI calculated Ambani's wealth on the strength of his holdings in Reliance