The country's top corporate house Tata Group's market capitalisation on Friday crossed the $100-billion mark, as some of its companies -- including IT giant Tata Consultancy Services -- gained value despite an overall weak market.

The cumulative market capitalisation of all the listed companies of Ratan Tata-led salt-to-software conglomerate rose to Rs 4,47,351 crore (Rs 4,473.51 billion), based on their share prices at the Bombay Stock Exchange.

Taking into account Friday's Reserve Bank of India reference rate for one US dollar at Rs 44.5855, this translates into total market valuation of $100.33 billion for the Tata Group.

The group's total market value stood at Rs 446,420 crore (Rs 4,464.20 billion), or $99.8 billion, on Thursday.

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The Tata Group comprises nearly 100 operating companies, but only about 30 of them are listed in the stock market. These include TCS, Tata Steel, Tata Motors, Tata Power, Indian Hotels, Titan, Voltas and Tata Communications.

TCS alone accounts for more than half of the group's total market value with a market capitalisation of $52 billion (Rs 232,194 crore or Rs 2,321.94 billion).

In an overall weak stock market on Friday, when benchmark Sensex fell by 83 points, some of the Tata Group companies managed to add value to their stocks. These included Rallis, Indian Hotels, Tata Communications, Tata Global Beverages, Tata Investment Corp, Trent and TCS.

Tata Group crossing the $100-billion dollar mark of market valuation, coincided with TCS's annual general meeting.

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Incidentally, Tatas had crossed Rs 1,00,000 crore (Rs 1,000 billion) market value mark with TCS's listing on August 25, 2004, becoming the country's most valued business house at that time.

Also, earlier in January this year, the Tata Group's market value had briefly crossed $100-billion mark, but a subsequent fall in the market brought down their valuation.

Way back in September 2007, the Mukesh Ambani-led Reliance Industries group had become the first business house in the country to attain a market cap of $100 billion.

About month later, RIL alone had attained a market cap of $100 billion on October 18, 2007, but a high rupee valuation was also a key factor at that time.

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RIL's market cap at that time had risen to Rs 4,07,748 crore (Rs 4,077.48 billion), which was equivalent to $103 billion according to the dollar rate at that time.

At the end of Friday's market, RIL had a market value of Rs 2,82,217 crore (Rs 2,822.17 billion), while its group valuation, after taking into account another listed company, RIIL was Rs 283,014 crore (Rs 2,830.14 billion) or $63.5 billion).

RIL shares on Friday fell by about 4 per cent, thus becoming a major drag for the benchmark Sensex.

The Mukesh Ambani-led group is currently the country's second most valued business house after Tatas, which is a reversal of position from a year ago. As on June 30, 2010, Tatas were second most valued with market cap of Rs 326,827 crore (Rs 3,268.27 billion), after Mukesh-led Reliance group's Rs 357,902 crore (Rs 3,579.02 billion).

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On stand-alone basis, Reliance Industries continues to remain the country's most value company, followed by Coal India, ONGC, TCS and Infosys.

Within the Tata Group, TCS is the most valued firm with a market cap of Rs 231,194 crore (Rs 2,311.94 billion), followed by Tata Steel (Rs 57,744 crore -- Rs 577.44 billion), Tata Motors (Rs 53,528 crore), Tata Power (Rs 31,023 crore -- Rs 310.23 billion) and Titan (Rs 18,954 crore -- Rs 189.54 billion).

A number of Tata Group stocks, such as Tata Motors, Tata Steel, Tata Tele, Titan and Voltas lost value on Friday, but gains in others like TCS, Tata Communications and Trent helped the group attain a market cap of over $100 billion.

Earlier in April this year, a brokerage report had said that TCS alone was on its way to double its market cap to over $100 billion in another four years.