According to the company's shareholding pattern filed with the exchanges, LIC held 276.39 million shares or 3.23 per cent stake in ONGC as on December 31, 2011.
This holding increased to 433.5 million shares or 5.06 per cent by February 8, according to Monday's filing.
This means the additional 157 million shares or 1.83 per cent were bought by the insurer between January 1 and February 8.
LIC's stake increase coincided with a significant run-up in the ONGC stock, which gained over 10 per cent during this period.
ONGC had ended the year 2011 at Rs 257.
But, by February 8, it was trading around the Rs 283 mark. An email sent to an LIC spokesperson seeking details of the market operation remained unanswered.
In last week's auction, the insurer picked up another 377 million shares, taking the total stake, 811 million shares, to 9.47 per cent, according to the company filing.
As of today, the insurer has bought a whopping 534.21 million ONGC shares in 2012, spending over Rs 15,000 crore (Rs 150 billion) in the process.
Of this, Rs 11,451 crore (Rs 114.51 billion) was spent in last week's auction, which happened at an average price of Rs 303.67 a share.
The insurer has pumped in at least another Rs 4,037 crore (Rs 40.37 billion), assuming the preceding open market purchase was done at the lower end of the price range Rs 257-283
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