Russia and China have failed to agree on a $400 billion natural-gas agreement that they have been working on for more than a decade.
Russian President Vladimir Putin said in Shanghai on May 20 after talks with Chinese counterpart Xi Jinping that the deal is in the "final phase" and negotiations will continue.
The deal -- expected to cover 30 years -- has been held up for years over price disagreements.
Gazprom officials said discussions were continuing nonstop in an effort to strike a deal before Putin leaves China on May 21.
Analysts say issues such as pipeline construction and prepayments may also be causing a delay in signing the deal.
Meanwhile, Russian and Chinese naval forces began joint maneuvers near Shanghai as Putin said Moscow and Beijing have agreed to coordinate their foreign policies "more closely" within international and regional organizations.
Putin called cooperation by the Russian and Chinese Defense Ministries a "serious factor of security" for the world.
Xi -- who along with Putin watched the start of the exercises -- said the manueuvers show "the unshakable determination...of China and Russia to together face new threats and challenges."
Putin said he hoped "the two militaries can strengthen cooperation under the new situation."
China said 14 Russian and Chinese ships will participate in weeklong exercises -- known as Joint Sea 2014 -- that include live-firing drills.
The military show with Russia comes amid China's territorial rows with Vietnam, the Philippines, and Japan.
The two countries also called, in a joint statement, for more regional and political cooperation on Ukraine.
Putin and Xi also focused on other economic issues.
Xi said the sides hope to increase bilateral trade to $100 billion by 2015. It was roughly $90 billion in 2013.
He added that economic cooperation will be expanded on "major projects," and a deal was signed to build a cross-border bridge over the Amur River from northeastern China into Siberia.
Another agreement was for construction of an oil refinery in the Chinese city of Tianjin and a liquified natural-gas project.
Putin, Xi, and UN Secretary-General Ba Ki-moon will attend the fourth summit of the Conference on Interaction and Confidence-Building Measures in Asia, due to open on May 21.
The conference's 24 members will include participation by top officials from Kazakhstan, Kyrgyzstan, Uzbekistan, and Tajikistan.
Based on reporting by Interfax, ITAR-TASS, and Reuters