According to the source, Iran will put about three million barrels back into storage in May, Reuters reported.
Loading figures for condensates and ultra-light crude, were not available for May.
In April, the country is expected to export 1.8 mbd of crude and a little over 370,000 bpd of condensates — down from a six-year high of nearly 2.9 mbd reached in February for both forms of oil.
In March, Iran loaded around 2.6 mbd a day of both crude and condensates, mostly the former, according to the source. No barrels of either crude or condensate were put in storage in March and April.
The final figures for February exports were significantly higher than preliminary numbers reported earlier by Reuters and show Iran took full advantage of its exemption from the production cuts by OPEC and non-OPEC producers, including Russia.
Still, Indian buyers are cutting purchases after state-owned refiners agreed to cut their annual imports deal with Iran by a fifth.
Crude liftings for India in May are expected to about 370,000 bpd, while in April Indian customers are lifting nearly 470,000 bpd of both crude and condensate.
Japan is scheduled to lift nearly 40,000 bpd in May, the lowest since March.
Loadings of crude and condensate for China this month are to hit a four-month low of a little over 500,000 bpd.