The government is expected to invite expression of interest (EoI) from bidders for Air India this month.
"While there is clarity on Air India's borrowings from financial institutions, its unpaid fuel bills and airport charges are likely to raise its liabilities," said an aviation ministry official.
He added the total liabilities could exceed the official estimate of approximately Rs 50,000 crore as it did not include outstanding bills.
The national carrier had a debt of Rs 51,890 crore as on September 30 last year as per provisional figures.
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Civil Aviation Minister Ashok Gajapathi Raju was quoted in an interview last month as saying that a debt figure of Rs 70,000 crores would not be surprising.
"When our exercise of calculating Air Indias debt began, we found that the sum was hovering around the Rs 50,000 crore mark. But I wont be surprised if the total debt reaches Rs 70,000 crore. Since people are looking at the books carefully, they may find more, he was quoted in a media report.
It will, however, not mention the reserve price for Air India, as per the official.
As part of reviving the ailing airline, the government decided on Air India's strategic disinvestment last year and a group of ministers, headed by Finance Minister Arun Jaitley, is working out the modalities of the stake sale.
Earlier this month, minister of state for Civil Aviation Jayant Sinha told reporters that at least 51 per cent of Air India's ownership will be transferred to the private sector and that the government's ownership will be 49 per cent or less.
Air India, its low-cost arm Air India Express and subsidiary AISATS would be one entity, while regional arm Alliance Air would be a separate entity.
Besides, Air India Air Transport Services Ltd (AIATSL) and Air India Engineering Services Ltd (AIESL) would be sold separately.