As soon as the price of oil rises above $100 US + per barrel for a protracted period of time it then becomes economic for synthetic oil and gasoline to be made from coal or natural gas. A company in South Africa called SASOL currently produces synthetic gas and diesel and oil from coal..
http://www.sasol.com/sasol_internet/frontend/navigation.jsp?navid=13500002&rootid=3 and supplies about 35% of South Africa's gasoline and diesel. The following is their 2009 presentation from the Howard Weil Energy Conference in New Orleans dated March 25, 2009:
http://www.sasol.com/sasol_internet/downloads/Howard%20Weil%20Energy%20Conference%20-%202009_1238077992064.pdf
So my point is that if the price of oil starts to significantly rise above $100 US per barrel for a long period of time it will become very economic for SASOL to build its plants in the USA to make gasoline and diesel fuel from the vast amounts of coal and shale natural gas in the USA.
Best Wishes; Scott