Iranian President Hassan Rouhani has announced the discovery of a field containing an estimated 53 billion barrels of crude oil.
The oil field in southwest Iran stretches over an area of 2,400 sq km (about 1,491 square miles) in the Khuzestan province and is around 80 meters (262 feet) deep, according to the Iranian leader.
It would be the country's second largest oil field, behind one in Ahvaz containing an estimated 65 billion barrels.
"We have discovered a new big oil field with 53 billion barrels of reserves," Rouhani said in a speech Sunday in the city of Yazd, according to the semi-official Mehr news agency.
"This is a small gift by the government to the people of Iran," he added, according to Agence France-Presse (AFP).
Iran, which is a founding member of the Organization of the Petroleum Exporting Countries (OPEC), currently has estimated proven crude oil reserves of 155.6 billion barrels, according to energy giant BP. The new discoveries would add about 34% to its total reserves.
The US Energy Information Administration (EIA) ranks Iran as the world's fourth-largest holder of oil reserves and the second-largest holder of gas reserves.
If the size of the new oil reserves is proven to be accurate, it would lift the country to third place, just below its regional foe Saudi Arabia.
Iran seized British-flagged oil tanker Stena Impero after an Iranian tanker was seized on suspicion of transporting oil to Syria.
Last month, Iran announced the discovery of a natural gas reserve that could create $40 billion in revenue. Rouhani said this latest discovery could boost the country's reserves by about a third.
The discoveries would be a lifeline for Iran's economy, which has suffered significantly under a series of US sanctions over the past year since the US withdrew from the Iran nuclear deal.
Rouhani attacked the US during his speech and said Iran is succeeding despite the punitive sanctions.
"We announce to America today that we are a rich nation, and despite your enmity and cruel sanctions, Iranian oil industry workers and engineers discovered this great oil field," he said, according to AFP.