Mikhail Khodorkovsky has been sentenced to nine years in prison after being found guilty of charges of tax evasion, fraud and embezzlement.
The billionaire founder of Yukos has been in prison since he was arrested in October 2003. His trial lasted 11 months, and judges took 12 days to read out the verdict.
But critics have claimed that the trial was politically motivated.
The news agency Interfax said US Democrat congressman Tom Lantos told reporters that he will table a draft resolution to Congress on "expelling Russia from the G8".
Lantos was reported to have said outside the court: "It seems that this political trial before a kangaroo court has come to a shameful conclusion.
"It is obvious that the conclusion of the trial was pre-determined politically and Mr Khodorkovsky could have been lef...