It is called BP Holding North America and the corp structure is outlined on page 175 of the 20-F.

FORBES: Time To Buy BP?

So BP sees Mr Fridman's resignation as part of a new campaign to put pressure on BP to organise a whole or partial buyout of their holding in TNK-BP.

BBC: BP and Russian oligarchs play chicken

Well BP believes that at least two of the oligarchs, Victor Vekselberg and Leonard Blavatnik, would like out - or at least they would like to convert their holding in the joint venture into cash and BP shares.

BBC: BP and Russian oligarchs play chicken