You have an erroneou perception that oil companies are insulated in those countries where they drill:
ARCO was a totally US company, with a totally domestic supply of crude. There was no foreign currency involved That's what you think. It would've been terrible if their finance department did not trade currency futures, and I would be VERY surprised if their shareholders and directors allowed that for long. Oil and gas are international markets, and even if you sell only in Montanta you are subject to price oscillations that are smoothed out by forward currency contracts. In addition, a domestic oil company tips into spot oil markets when they are short in supply or have excess volume.
and no foreign markets either, to drive up the price of oil. The price for oil was not determined by ARCO. It was determined by demand and AGGREGATE supply.
BP stated at the time of the take over that they wanted to see a single price for oil in all their markets, that they hoped to raise the price of gasoline in the US to the same price that they pay in Europe. And you thing that ARCO, being good Americans they were, would not want the same thing?
In addition, you misunderstood what BP said: it is a well-managed company and I cannot believe that someone could say such a silly thing, which would cause laughter even in an MBA class...