Infosys surpassed Reliance after the close of markets on Friday, rising 4.7 percent, while the energy conglomerate gained 0.4 percent.
Infosys' weight in the benchmark index has increased to 9.05 percent from 8.74 percent as of Friday's close, while that of Reliance fell to 8.69 percent compared with 8.76 percent earlier.
On Monday, Infosys shares are up 0.9 percent while Reliance gains 0.72 percent.
ITC Ltd (ITC.NS) continues to enjoy the biggest weight of 10.74 percent in the Sensex.
Last week IT major Infosys reported a 1.6 % rise in consolidated net profit to Rs 2,407 crore for the second quarter ended September 30, 2013, on the back of large deals and increased sales from Big Data and Cloud.
The Bangalore-based firm had reported a net profit of Rs 2,369 crore in the year-ago period, it said in a BSE filing.
Consolidated revenue was up 31.5 % to Rs 12,965 crore from Rs 9,858 crore in the year-ago period.