Rosneft allocated seven cargoes of 100,000 tonnes each loading between May 15 and 31 to IOC, according to the traders.
In May IOC will load Rosneft-sourced Urals oil volumes from Baltic ports for the first time. Previously the major buyers of the cargoes were trading firms Vitol and Trafigura.
However, international traders will stop purchases of oil from Rosneft after May 15 as EU sanctions over several Russian companies come into effect.
Last December IOC and Rosneft signed a term contract for supply of up to 2 million tonnes of Urals oil until the end of 2022.
Under the agreement IOC has bought several Urals cargoes from the Black Sea port of Novorossiisk this year.
It was not immediately clear if the May supplies come as a part of the existing contract or as a part of the new agreement.
Last week Reuters sources said that Rosneft was negotiating supply deals with several Indian refiners including IOC.
Rosneft and Indian oil representatives did not immediately reply to Reuters requests for comment.
India has asked state-run energy companies to evaluate the possibility of buying European oil major BP’s stake in sanctions-hit Russian firm Rosneft, two people familiar with the matter said in late April.