Just stumbled on an article, according to which the "supply & demand" numbers were skewed throughout 2015 by falsely showing more "supply" than there actually was - thereby depressing the price.
In French from Russian website.
https://fr.sputniknews.com/international/201603181023469993-petrole-prix-effondrement-raison/
And here's the Wall Street Journal
http://www.wsj.com/articles/crude-mystery-where-did-800-000-barrels-of-oil-go-1458207004
Crude Mystery: Where Did 800,000 Barrels of Oil Go?
(edit = that's 800,000 Barrels EVERY DAY !!!)
Tally of unaccounted-for oil hit highest level in 17 years in 2015; oil data is ‘an imperfect science’
By
Georgi Kantchev
Updated March 17, 2016 9:12 p.m. ET
There is mystery at the heart of the oversupplied global oil market: missing barrels of crude.
Last year, there were 800,000 barrels of oil a day unaccounted for by the International Energy Agency, the energy monitor that puts together data on crude supply and demand. Where these barrels ended up, or if they even existed, is key to an oil market that remains under pressure from the glut in crude.
Some analysts say the barrels may be in China. Others believe the barrels were created by flawed accounting and they don’t actually exist. If they don’t exist, then the oversupply that has driven crude prices to decade lows could be much smaller than estimated and prices could rebound faster.
Whatever the answer, the discrepancy underscores how oil prices flip around based on data that investors are often unsure of.
Barrels have gone missing before, but last year the tally of unaccounted-for oil grew to its highest level in 17 years. At a time when the issue of oversupply dominates the oil industry, this matters.
“If the market is tighter than assumed due to the missing barrels, prices could spike quicker,” said David Pursell, managing director at energy-focused investment bank Tudor, Pickering, Holt & Co.