The deal was signed between Venezuelan President Nicolas Maduro and Rosneft CEO Igor Sechin, in Caracas.
Sechin also discussed Rosneft infrastructure collaboration with Venezuelan state energy company PDVSA, according to the statement.
The terms of the agreement guarantee that the wholly-owned Rosneft branch of Grupo Rosneft will operate the southern Caribbean Patao and Mejillones offshore gas fields for 30 years.
Rosneft will be able to sell all oil and gas extracted from the fields, including liquefied natural gas. Total reserve estimates for the two fields are said to be about 180 billion cubic meters (bcm) of gas.
Venezuela's rapid dissolving socialist government has turned to longtime ally Russia for the cash and credit necessary to survive.