Abramovich started his commercial activity in the late 1980s when Soviet president Mikhail Gorbachev's reforms permitted the opening of small private businesses, known as co-operatives. In 1992 to 1995 Abramovich founded five companies that conducted resale and acted as intermediaries, eventually specializing in the trading of oil and oil products. In 1995 Roman Abramovich, together with Boris Berezovsky, acquired the controlling interest in the large oil company Sibneft. The deal was within the controversial loans-for-shares program and partner paid $100m for half of the company, only slightly below the stake's stock market value of $150 million at the time. The fast-rising value of the company led many observers, in hindsight, to suggest that the real cost of the company should have been in the billions of dollars.
During the 1990s, through their holding company Millhouse Capital, Abramovich and his business partner Eugene Shvidler acquired significant stakes in Russia's largest air company Aeroflot and several aluminium plants from Trans World Group owned by David and Simon Reuben which were merged with the metals assets of Oleg Deripaska to create the aluminum giant Rusal. Millhouse LLC, as it is now known, also invested in several smaller companies in the automobile industry, pharmaceuticals, food processing, real estate and other sectors.
Millhouse divested itself of several key assets in 2002–2005. Most notably, the company sold its stake in Sibneft to state energy giant Gazprom for $13 billion, and its stake in Rusal to Oleg Deripaska for $2 billion. In 2006, Millhouse reinvested some of the proceeds by acquiring a 41% stake in Evraz Group, Russia's largest domestic steelmaker and one of the top 10 internationally.
In 2004, Swiss criminal investigators abandoned an investigation into an alleged fraud involving a $4.8 billion loan from the IMF to Russia, in which Abramovich was one of the investigators' key suspects, after the United States and Russia refused to divulge information on the scandal. No evidence linking Abramovich to the IMF funds was ever reported.
Despite maintaining that his primary residence is Moscow, Abramovich was named the second-wealthiest person in the UK in the Sunday Times Rich List 2006, with an estimated fortune of £10.8 billion. Abramovich qualified for the list by virtue of retaining residences in Knightsbridge, London, and Sussex. His 440-acre estate in West Sussex was previously owned by King Hussein of Jordan. It has a swimming pool, a clay pigeon shoot, a rifle range and a go-kart track.