Venezuelan Oil Minister Rafael Ramirez, president of the state oil company known as PDVSA, signed the agreement in Venezuela's Bolivar state.
The companies will operate the Carabobo sites in Venezuela. PDVSA estimates production there should reach 120,000 barrels of oil per day by 2017.
Ramirez added that additional work was planned in the Gulf of Venezuela.
Rosneft will control 40 percent of the joint venture. It said it would extend a $1.5 billion loan and a separate $1.1 billion bond to Venezuela to help finance operations there, state news agency RIA Novosti reports.
Venezuela has some of the largest deposits of crude oil in the world. The Orinoco belt, which includes Junin-6, is considered one of the biggest reserve areas outside of the Middle East.
State-owned Rosneft this year acquired private Russian oil company Surgutneftegas's stake in a consortium managing the Junin-6 oil field.
Rosneft in January announced plans to invest around $10 billion to support its work in the Venezuelan energy sector.