Things I have considered:
Poor economic conditions around the world could have caused an unpredicted decrease in demand. The resulting surplus has begun driving prices down.
This could be exacerbated by a decade of record-high prices that spurred massive investment that changed supply capacity. I know part of this could also be a result of technological innovation that, over the last few years, has changed supply capacity. Add to this the relatively recent discovery of new pockets of oil/natural gas here that producers have begun exploiting.
Consumer's expect prices to continue falling and so they forgo purchasing fuel if possible. This slowdown in demand can actually help fuel that expected price drop. This could contribute to a steady downward pressure, I think.
Geopolitical relations between America, Saudi Arabia, Russia and Iran. I know that Saudi Arabia and co. could slash production in an attempt to remove the excess supply and drive prices of oil up again.
America is now a (the?) leading oil producer world wide and the USA do not import nearly as much oil as it once did. The fact that the USA are using oil extracted and refined domestically has obvious implications etc. An interesting question is how OPEC's recent announcement to not cut production and instead let prices stay low might affect domestic production where things like horizontal drilling and fracking drive up the cost of extraction.
I would really appreciate a substantiated walkthrough of what has caused this very sharp turn around in oil prices. I know the last decade was a time of record highs...so why now the massive landslide in the value of oil?
I should say I am hoping to hear from economists who perhaps have some specialized knowledge here. I do have an undergrad degree in economics and I have read and am familiar with most of the general arguments. I am looking for a well substantiated and thorough answer that will deepen my understanding of this issue.