There have been various stories about why the Polish company bought Mažeikių Nafta in Lithuania after the Russian company that owned it - Yukos - was taken over by the Russian government. Some said that the Polish company wanted to expand; some others - that the Poles felt and still feel brotherly feelings to Lithuania (we've been a country of two peoples - Rzeczpospolita Obojga Narodów - for more than 400 years) and therefore want to invest there.
Later on, there were some accusations that Lithuania does not give preferential treatment to the company, to which Lithuanian Prime Minister Mr. Kubilius answered that the state cannot give preferential treatment to one company and not give to another. There was pressure from one government on another, which was further soured by the spelling issue and claims about minority rights in Vilnius/Vilna/Wilno region. V. Savukynas also provides a good article here.
I do not know if this is over, but recently in Lithuanian press showed up a story that that quotes WikiLeaks to explain why the Polish company came to Lithuania. The story is long, but the idea is that if Mažeikių Nafta were bought out by some Russian company, PKN Orlen would have likely become bankrupt in 4-5 years. So this is a pre-emptive strike in order to buy some time and use Lithuania in pressing Russia to repair the pipeline "Druzhba". Now I do not know if this is true, but to me it sounds reasonable.
Any opinions or insights?