Russia will help India build at least 10 more nuclear reactors, Indian Prime Minister Narendra Modi has said following a visit by Russian President Vladimir Putin.
The two countries signed a series of major energy agreements on Thursday.
Russia will also remain India's top defence supplier, said Mr Modi.
Mr Putin's visit to Delhi comes as India faces energy shortages and Russia seeks to expand its ties with Asia in the face of Western sanctions.
Mr Modi said that the two countries had outlined an "ambitious vision" for nuclear energy during the talks and that the new reactors would be built over the next 20 years.
He added that, under the deal, nuclear components would be made in India.
A $1bn (£630m; €800m) joint venture to support hydro-electric power projects in India has also been agreed, according to Reuters news agency.
Meanwhile Russian oil producer Rosneft signed a deal to supply India with 10 million tonnes of oil per year, Reuters said.
Mr Putin said earlier that his country was looking to export more Russian oil and gas to Asia because of problems with the European market.
A project to build a new gas pipeline to Europe, known as South Stream, was cancelled last week amid concerns that it could be in breach of EU competition rules.
Also, the crisis in Ukraine has led to a bitter fall-out between the West and Russia, which has been placed under wide-ranging sanctions by the US, EU and several other countries.
The BBC's Sanjoy Majumder in Delhi says that Russia will continue to be an important defence supplier to India despite the fact that it has lost a couple of lucrative contracts recently to the United States and Europe.
One of several defence deals is a plan by Russia to manufacture its most advanced military helicopter in India.
Russia and India were close allies during the Cold War but in recent years the relationship has been more tense.
India is reported to be upset with Russia for selling attack helicopters to Pakistan and Russia has been unhappy with India for choosing French Rafale fighters and American Apache attack helicopters over Moscow's defence products.
Later today, Mr Putin will meet business leaders and attend a diamond conference in Delhi.
The two countries are expected to sign an agreement on improving bilateral diamond trade.
Russia is the top producer of rough diamonds in the world and India is the global hub for cutting and polishing the gemstones.
But Russian mines sell most of the rough produce to the diamond hubs of Antwerp and Dubai from where it comes to India, something that Delhi wants to change.