Mr Berezovsky - who attended court for the ruling - told the trial Mr Abramovich had "intimidated" him into selling shares in a Russian oil company at a fraction of their value. He also told the judge Mr Abramovich had broken a promise made during a deal relating to a Russian aluminium company.
Mr Abramovich disputed the claims, saying they were "wholly without merit".
Both men "rose to enormous wealth and influence" in Russia in the 1990s as state-owned firms were privatised in the wake of the collapse of communism, the court heard.
But Mr Berezovsky fled Russia, never to return, in late 2000, after falling out with president Vladimir Putin. He travelled initially to France, then settled in England. He claimed that he had been betrayed by his former friend and business partner.
Announcing her decision, Mrs Justice Gloster said she found Mr Abramovich "to be a truthful, and on the whole reliable, witness". She said she dismissed Mr Berezovsky's claims both in relation to Sibneft and in relation to RusAl "in their entirety".