20$ a barrel of oil.

Won't happen.
Victor Davis Henson writes:

...and collapse the world oil market though conservation, more exploration, alternative fuels, and nuclear power. 20 -dollar-a-barrel oil will take immediately nearly $500 billion a year out of the coffers of Middle East exporters—and with that loss, floating petrodollars for weapons and terrorists.

Get real people ! 20$ a barrel oil won't happen. Not in the next 30-50 years (probably never). All alternate energy sources known to us cost about $100 per barrel, equivalent. Oil is cheap, nothing comes near that.
As much as we would love to deprive those terrorism mongering nuts of their income - it won't happen. You need to think up some other terror fighting, planet saving, strategy.

Nuclear is the most promising energy source, but there won't be a new reactor going on line for at least 30 years, even in the unlikely scenario that someone decides to build one today.