Financial terms of the deal were not released.
The remaining 70% interest in the blocks will be held by ExxonMobil, who is also the operator of the blocks.
Of the 20 blocks, 17 are situated in the western Gulf of Mexico and the rest three are in central Gulf of Mexico. The blocks are spread over an area of 111,600 acres in water depths ranging between 640m and 2,070m.
The company acquired interest in Alaminos Canyon 569, 612, 613, 655, 656, 657, 698, 699, 700 and 701; East Breaks 429, 471, 472, 473 and 515; Keathley Canyon 529 and 573 blocks located in Western Gulf of Mexico.
The Central Gulf of Mexico blocks are namely Walker Ridge 629, 673 and 717.
The acquisition of stake in the blocks is a part of the Strategic Cooperation Agreement signed by Rosneft and ExxonMobil in 2011.
As per the agreement, the two companies and their subsidiaries will undertake joint exploration and development of hydrocarbons in Russia and other countries.
Rosneft president Igor I Sechin said, "This agreement provides Rosneft and its subsidiaries with access to one of the world’s most prolific basins. We believe joint efforts of our companies will ensure the most efficient development of these blocks, with application of the latest technologies and adhering to high environmental standards."