Indian billionaire Mukesh Ambani's Reliance Industries, which is investing in a historic U.S. oil refinery project proposed by President Donald Trump, has now emerged as the biggest buyer of Venezuelan crude outside the U.S.

Trump has been pushing India to buy more Venezuelan oil, but while state-owned oil companies are making opportunistic purchases, Reliance has been the primary buyer, according to Kpler data shared with CNBC. It shows that outside the U.S., India is the biggest destination for these supplies, with Reliance purchasing the bulk of that crude.

"Reliance's Jamnagar complex has been the main destination for Venezuelan crude in India, and we expect it to remain the primary buyer," Sumit Ritolia, lead research analyst at Kpler, told CNBC.

In September, India imported 257,000 barrels per day of Venezuelan crude, of which 76% went to Reliance Industries, data showed. The Jamnagar refinery is the world's "largest and most complex single-site refinery" with crude processing capacity of 1.4 million barrels per day, according to Reliance.

Venezuelan heavy and extra-heavy grades of crude are relatively difficult barrels to process and are not universally suitable across India's refining system, Ritola said, adding that the Jamnagar complex is particularly well configured for these barrels.

In March, Trump had announced that the U.S. will build its first refinery in 50 years with investment from India's Reliance Industries. The president had thanked Reliance for this "tremendous investment."

While Reliance has not confirmed the size of investment, Trump in a Truth Social post had said that "THIS IS A HISTORIC $300 BILLION DOLLAR DEAL — THE BIGGEST IN U.S. HISTORY."

Reliance is the most valued company in India, with a market capitalization of more than $169 billion.

Reliance's Venezuelan purchases come at a time when India's procurement of Russian oil has drawn the ire of the U.S., where lawmakers have given Trump the power to impose up to 100% tariffs on countries buying energy from Moscow.

Despite mounting pressure to buy more energy from the U.S. and cut its dependence on Russian oil, the Indian government has insisted that its decisions are driven by the need to ensure energy security for its people.

While oil supplies in September from Russia to India have "moderated" from exceptionally high levels in June and July, that is largely driven by the stronger competition between Beijing and New Delhi and not the threat of tariffs, Ritolia said.

India is the largest destination for Russian crude, securing a supply of 1.82 million barrels per day in September versus China's 1.49 mbd, according to Kpler data, much more than Venezuelan purchases.

For October, 350,000 barrels per day of crude supplies from Venezuela are bound for India, though some of these could land in November because of the long voyage time, Ritolia said.