Essar Oil, Iran's key Indian client, imported about 21 percent more oil from Tehran in 2015/16 as it stepped up shipments in the last quarter of the year after western sanctions against Tehran were lifted.
Essar shipped in 204,500 barrels per day (bpd) of oil from Iran last month, a jump of 66.3 percent from February, according to tanker arrival data obtained from trade sources and ship-tracking services on the Thomson Reuters terminal.
The private refiner skipped purchases from Iran in March 2015 under pressure from sanctions.
Essar's oil imports from Iran averaged at about 120,000 bpd in the year to March 31, 2016, the data showed.
Iran's share in overall imports by Essar Oil in the last fiscal year rose to about 37 percent from about 28 percent a year earlier.
In the last fiscal year, Indian refiners shipped in 14.4 percent more oil from Iran at about 251,100 bpd, the data showed.
The increase was the largest since the 2007/08 fiscal year, according to Reuters data.