How ISIS smuggles its oil

Israel has been secretly buying oil through the Turkish port of Ceyhan, which is supplied by the oil pipeline from Iraqi Kurdistan, the Israeli daily Haaretz reported on April 10.

According to Haaretz, in November Samir Madani, a Kuwaiti oil trader, noticed some oil tankers, heading to the Suez Canal from Turkey's port of Ceyhan. It stopped somewhere in the eastern Mediterranean outside Israel's territorial borders, turned off its identification transponder and "resurfaced" a few days later, "mysteriously" lighter than when it had left Ceyhan. Then the vessel sailed to Cyprus and returned to Turkey, loaded up on oil that had come from the northern Iraq and repeated the journey, including the act of disappearing.
"His conclusion was that the Valtamed had been shipping oil that wasn't recorded anywhere to a country that wasn't supposed to buy it - in other words, Israel was secretly buying Kurdish oil through Turkey," Haaretz wrote.
Haaretz also reported another similar incident quoting the website TankerTrackers.com [Madani is its Co-Founder]. It affirmed that a tanker called Kriti Diamond "turned into" Kiton and offload oil in Israel. Then it transformed in its original identity to sail back to Turkey.
"It is with great pride that we present you the missing KRITI DIAMOND, currently operating under her new pseudonym: KITON," the site wrote on February 16.

'The MARIKA/KRITI DIAMOND forgot to take off her disguise as KITON after leaving Ashkelon empty", four days later they tweeted.
Addititionally, TankerTrackers.com noted that the Mabrouk oil tanker, left Ceyhan, then was masked as the Maro near the Israeli shore. After a few days appeared again as the Mabrouk.

It's interesting to note that a similar method was used by Tel Aviv when it was allegedly buying ISIS oil.

On November 30, 2015, the Israeli newspaper Globes wrote that Kurdish and Turkish smugglers were transporting oil from the ISIS-controlled territory in Syria and Iraq to the Kurdish city of Zakhu in a triangle of land near the borders of Syria. Then, this oil was sold to Israel through Turkey.

Globes reported (source):
In August, the "Financial Times" reported that Israel obtained 75% of its oil supplies from Iraqi Kurdistan. More than a third of such exports go through the port of Ceyhan, which the FT describe as a "potential gateway for ISIS-smuggled crude."

"Israel has in one way or another become the main marketer of ISIS oil. Without them, most ISIS-produced oil would have remained going between Iraq, Syria and Turkey. Even the three companies would not receive the oil if they did not have a buyer in Israel," an industry official told the newspaper "al-Araby al-Jadeed."

"Israel has in one way or another become the main marketer of IS oil. Without them, most ISIS-produced oil would have remained going between Iraq, Syria and Turkey," the industry official added.
It's interesting to note that in the both cases Turkey and a pipeline between it and Iraqi Kurdistan are a key part of the "unofficial" oil supplies.

When the Kurdistan Regional Government (KRG) held an an independence referendum in 2017, the Turkish leadership threatened to impose a blockade on the oil supplies from Iraqi Kurdistan halting the main source of the KRG financial revenue. However, this was not done.
The 2017 independence referendum in Iraqi Kurdistan caused a signficiant political crisis in Iraq and triggered a limited military operation by the Iraqi Federal Government against KRG forces. As a result the KRG obtained no independence and even lost the oil-rich area of Kirkuk.
As to the ISIS oil business, the oil supplies from the ISIS-held area through Turkey was halt only thanks to a large-scale Russian military capaign against the terrorist group's oil infrastructure and a major diplomatic and media campaign aimed at pressuring Turkey.