Currently, Gazprom, Russia's state-run natural gas company, holds a 100 percent stake in Sakhalin-3's main drilling area.
Gazprom is negotiating with multinational oil firm Royal Dutch Shell about drilling methods and other details, aiming for the joint development of Sakhalin-3.
If they reach an agreement, Mitsubishi and Mitsui would highly likely join the development.
The two trading firms have jointly worked with Shell on the Sakhalin-2 project, which the two firms hold a combined 20 percent stake.
In addition, Mitsubishi and Mitsui have agreed with Shell to jointly engage in future development projects in Sakhalin.