For the week ended November 9, total market capitalisation of the 10 most valued companies plunged to Rs 9.90 lakh crore from Rs 18.88 lakh crore in the preceding week.
During the week, ONGC's valuation plummeted by Rs 7,357 crore to Rs 2,19,961 crore, while that of RIL tumbled by Rs 6,360 crore to Rs 2,55,021 crore.
ONGC last week reported its a 32 per cent drop in its September quarter net profit, weighed down by rising costs and subsidy burden.
Coal India was another major loser whose valuation declined by Rs 2,652 crore to Rs 2,18,704 crore.
State-owned NTPC saw a value erosion of Rs 824 crore to Rs 1,37,658 crore.
On the other hand, mortgage lender HDFC emerged as the biggest gainer with its market capitalisation rising by Rs 4,225 crore to Rs 1,22,304 crore.
FMCG major ITC saw a climb of Rs 4,007 crore in its valuations to a total of Rs 2,26,850 crore.
In the banking space, SBI and HDFC Bank witnessed an increase in their respective market capitalisation. HDFC Bank's valuation rose by Rs 2,109 crore, while that of SBI grew by Rs 258 crore to Rs 1,44,700 crore.