Yukos ex-CEO Mikhail Khodorkovsky has asked the Russian Supreme Court to overturn his second conviction and release him from custody.
Khodorkovsky is taking part in Tuesday's appeal hearing at the Supreme Court by video link.
Following their two trials, Khodorkovsky and his former business partner Platon Lebedev each faced an 11-year prison term.
Khodorkovsky's actual sentence is calculated from October 25, 2003, when he was arrested, and Lebedev's sentence is calculated from July 2, 2003.
The former Yukos head could be released from prison in about a year and two months, and Lebedev could be released in less than 11 months.
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