This massive surge in exports comes ahead of the May 8 of US president's decision to cancel Iran nuclear deal and impose imminent sanctions targeting the country's oil exports.
Sources have also said the rise in exports last month was a way for Iran to prepare itself for a more challenging environment.
Demand for Iranian crude in China and India is likely to remain very strong even if sanctions are now due to be imposed, though refiners in Europe, South Korea and Japan are likely to tread more carefully.
Total estimated export volume on Aframaxes, Suezmaxes and VLCCs from Iranian ports in April rose 16% to 2.70 million b/d from 2.32 million b/d in March, according to data from S&P Global Platts trade flow software cFlow.
The sharp rise in exports is attributed to refinery turnaround work at the Abadan refinery along with floating storage volumes being exported to some of Iran's key customers.
Of this, crude exports were around 2.45 million b/d, a rise of some 400,000 b/d from March, though condensate exports remained largely steady month-on-month.
Asian flows rise
Exports to Asia rose significantly to 1.81 million b/d in April from 1.40 million b/d in March, accounting for 67% of total monthly exports, up from 60% in March.
The Asian gain was led by a rise flows to India, up by almost 60% to 670,500 b/d.
Indian demand for Iranian crude is rising steeply as both Indian state-owned and private refiners are buying more due to Iran offering the country some freight discounts.
India's oil ministry has indicated that its imports of Iranian crude for the fiscal year 2018-19 will rise by more than 30% from the previous year.
China remained the largest export destination for Iranian oil, with flows rising to 714,467 b/d in April, up just over 20,000 b/d from March.
Even demand from Japan, which has fallen sharply in the past year, rose from no volumes in March to 118,900 b/d in April.
Flows to South Korea and Japan, which mainly consist of condensates, have declined in the past few months, as Iran has been consuming more volumes domestically at its Persian Gulf Star refinery.
Flows to Europe in April fell to 716,732 b/d from 761,418 b/d, as interest from Turkey, Italy, Spain was slightly lower.
Earlier in the week, National Iranian Oil Company sold 2.88 million b/d of oil and gas condensates to April, with crude accounting for 2.62 million b/d.
Iran's previous highest post-sanctions crude exports were 2.44 million b/d in October 2016, the report said.
Iran has doubled its oil exports since the landmark deal with Western powers to lift sanctions on its oil industry was implemented in January 2016.
After four years of crippling curbs on its oil exports, Iran surprised most by ramping up production and broadening its customer base in Asia and Europe.
Exports averaged 2.12 million b/d in 2017, compared with just 1.13 million b/d in 2015, when the sanctions were still in place, he report added.