Somali pirates relinquished control on Saturday of a South Korean oil tanker they have held since April, having received a $9.5 million ransom payment.

That appears to be the highest sum ever paid to pirates, surpassing a $7 million ransom payment made in January.

The South Korean tanker had held $170 million worth of Iraqi crude oil. Twenty-eight other vessels and about 500 hostages remain under control of Somali pirates.