Rosneft, the Russian oil group that is planning one of the world’s biggest and most controversial initial public offerings, on Monday warned potential investors that they face numerous risks.

The group’s preliminary prospectus, a copy of which was obtained by the Financial Times, contains 25 pages of “risk factors” – including those stemming from the controversial acquisition two years ago of Yuganskneftegaz, its main asset. Yuganskneftegaz was purchased in a forced auction from Yukos, the company built by the jailed oligarch Mikhail Khodorkovsky.