Wonder what caused/is causing the volatility that seems to be increased since about 1999?
Lots and lots of tail production. Some of us predicted that because of the short life cycles of wells owing to poorer quality prospects and higher quality completions that deplete the wells faster and of course shale... that the cycles would be of higher frequency and amplitude. Add to the physical factors mentioned the fiscal factors of trading and oil becoming firmly entrenched as a commodity with the expectation that 1% over supply is a glut and the same 1% shortage is a disaster and this high frequency high amplitude pricing is what you get.
Oil as a commodity isn’t like crops that just have one set of output variables each year..... oil can change constantly and does. It has no real season.