According to a study from Purdue University the threshold at which electric cars in California become economical is when oil hits between $171 and $254 per barrel. The highest price oil has ever reached was in June 2008, when it went above $140 a barrel. The previous peak was in December 1979, when a barrel of crude was more than $100, adjusted for inflation.
That threshold oil price drops considerably when the price of electricity is lower. Indiana, for example, averages a flat rate of about 8 cents per kilowatt hour and the oil price need only be in the $100 per barrel range.