>What's to stop multiple Russian companies from buying 10% each and voting as a group?

As Zsolt Hernádi said, it is a theoretical possibility. There would be several ways to do that, but none too easy. For example, the free float is only 29.8% of the whole, try to buy up 10% on the open market bound to drive up the price substantially. You could buy other blocks, but, if the OMV – Surgutneftegas deal is an indicator, that also would prove to be an expansive proposition.