The deal could be announced as soon as Monday, with S&P set to pay around $44 billion in stock, according to a report in The Wall Street Journal.
S&P Global and IHS did not immediately respond to Reuters' requests for comment.
At that price, it would be the biggest deal of 2020 and a sign deal-making activity is accelerating as breakthroughs in Covid-19 vaccine-related developments improve the economic outlook.
S&P Global is renowned for providing debt ratings to countries and companies, as well as data on capital and commodity markets worldwide. It became a standalone business in 2011 when its then parent McGraw-Hill separated S&P from its education business.
IHS Markit was formed in 2016 when IHS, whose businesses range from data on automotive and technology industries to publishing Jane's Defence Weekly, bought Markit in 2016 for around $6 billion. Markit, founded by former credit trader Lance Uggla, provides a range of pricing and reference data for financial assets and derivatives.
IHS has a market value of around $36.88 billion based on the stock's last close on Friday, Reuters calculations showed, with its share price up around 22% so far this year.
The transaction is likely to face close examination from competition watchdogs, as the market for financial information becomes increasingly concentrated.
The London Stock Exchange is in the final stage of trying to win clearance for its planned $27 billion acquisition of data provider Refinitiv, which has been through a long review process by the European Union's Competition Commissioner.
Refinitiv was carved out of Thomson Reuters by private equity-giant Blackstone in 2018, when it bought a 55% stake in the business in its biggest bet since the 2008 financial crisis. Thomson Reuters, parent of Reuters News, retains a 45% holding in the business.