Mr. Khodorkovsky, 41, who had been the wealthiest man in Russia until he publicly challenged President Vladimir V. Putin, was found guilty of six charges, including fraud and tax evasion.
Under the terms of his sentence, his remaining prison term will be reduced by the 19 months of pretrial confinement he has already served, and it will end in 2012. Platon Lebedev, a Yukos colleague and fellow defendant, was given the same sentence. Prosecutors had asked for maximum sentences of 10 years.
The court also ordered the two men to pay about $613 million in taxes and fines. A third defendant, Andrei Krainov, was convicted and given a suspended sentence of five and a half-years.
The verdicts were read just before 1 p.m. in a small crowded courtroom near Moscow's center. After the judges called for all to rise and the sentences were handed down, the chief judge asked the two men if they understood the charges and their resolution, according to pooled reports of the journalists allowed into the room.
Mr. Khodorkovsky called the results "a monument to Basmanny justice," referring to the name of the local court where the charges originated and where his defense team claims a rigged prosecution began.
Mr. Lebedev's tone was biting. "Any normal person would not understand," he said.
In the small area where spectators could stand, Mr. Khodorkovsky's wife sobbed, comforted by his father. As word of the verdicts rippled outside the court, protestors supporting the Yukos officials and kept far from the court entrance by a contingent of guards, began chanting, "Lawlessness!" "Not Guilty!" and "Shame!"
Another group of demonstrators, this one pro-government, was almost silent. In interviews, several did not seem to know why they were there, suggesting they had been brought to the court by an interested party.
The sentences end, for the moment, the rout of Mr. Khodorkovsky, several associates and the Yukos oil company, which lost its core asset in an auction last year - one that was also widely criticized as Kremlin-rigged. Prosecutors, however, said more charges were expected. They did not offer details.
Mr. Khodorkovsky was variously regarded in Russia as a victim of Kremlin vindictiveness or a ruthless and unsavory speculator who amassed his almost uncountable fortune on insider deals. Having financed opposition parties, he appeared to have political ambitions of his own.
The energy tycoon once led a company that employed more than 100,000 people and pumped more crude oil than the nation of Libya. As his company's market share grew, he emerged as a player on the world's energy stage.
Since his arrest in the fall of 2003, Mr. Khodorkovsky's lawyers and supporters have said that the case against him was largely driven by political motivations and Kremlin pique. They characterized the legal actions against him and the company he founded as Moscow's update on the Communist Party's infamous show trials of old.
In his first term, Mr. Putin made clear his deep animosity to the class of extraordinarily wealthy businessmen, known here as oligarchs, who made their fortune during the period when the vast assets of the Soviet state were privatized. Mr. Putin has since made peace with several of them, but never Mr. Khodorkovsky, who was a critic of Russia's centralized state.
There was public silence from the Kremlin today in the hours after the verdicts were read.
Western governments, including the United States, have warned that Russia's handling of the case raises questions about the Kremlin's commitment to a stable business environment and the rule of law.
The scene in the Meshchansky Court, where Mr. Khodorkovsky was convicted, had long been predictable, as he and Mr. Lebedev, who had been arrested by masked gunmen, were kept before the panel of judges in a gray metal cage.
And after 12 mind-numbing days of reading the verdict, the judges had spent most of their time this week dismissing much of Mr. Khodorkovsky and Mr. Lebedev's grounds for defense.
Lawyers for both men said this appeared to be a pre-emptive effort to undermine any appeals, which the two men have 10 days to file.
The battle for the perception of the case began immediately. Yukos issued a statement declaring the verdicts "a gross travesty of justice produced by a judicial system that has not only been content to be maneuvered to destroy Mikhail Khodorkovsky but also is intent on bringing down Yukos."
Expressing some sentiment from the United States Congress, Representative Tom Lantos, a California Democrat, who sits on the House International Relations Committee, appeared outside the court and was harshly critical of the verdicts.
"This political trial, tried before this kangaroo court, has come to a shameful conclusion," Mr. Lantos said. "The conclusion of this trial was predetermined politically."
Mr. Lantos said he would reintroduce a motion to exclude Russia from the Group of Eight industrial nations, a proposal the White House has previously opposed. He also said he and his colleagues would keep a close eye on any appeals.
The denunciations by Yukos and Mr. Lantos were joined by voices throughout Russia's small opposition, but were also met by unequivocal statements of support for the verdicts from people in Mr. Putin's circle.
Sergei Mironov, the speaker of the upper house of Russia's Parliament, a body largely compliant with Mr. Putin, said the verdicts were exactly as expected.
"I would not have understood it if the court had acquitted Khodorkovsky," Mr. Mironov told the Interfax news agency. "Then I would have become doubtful about the prosecutor general's office."
Mr. Khodorkovsky, in a statement read outside the courthouse by one of his lawyers, said he would try to maintain a public profile from prison, and would underwrite foundations supporting poetry, philosophy and prisoners in Russia.
As a man who now appears to have become the world's wealthiest convict - the Russian edition of Forbes magazine estimated his wealth this year at $2 billion, well below the $15 billion he was once thought to possess - he seems to have the resources to keep his name in the news.
Mr. Khodorkovsky also made clear his feelings about the case. "I know that my conviction was decided in the Kremlin," his statement said. "Some in the president's entourage insisted that only an acquittal would inspire society's trust in the authorities. Others believed I should be put in prison for a long time to deprive me of any capacity to fight for freedom."
"To the first group, I would say, 'Thank you.' And I would like to inform the others that they have not won. I will fight for freedom."