After the first OPEC oil production cut in eight years took effect in January, oil traders from Houston to Singapore started emptying millions of barrels of crude from storage tanks.

Investors hailed the drawdowns as the beginning of the end of a two-year supply glut - raising hopes for steadily rising per-barrel prices.

It hasn't worked out that way.

Now, many of those same storage tanks are filling back up or draining more slowly than investors and oil firms had expected, according to global inventory estimates and more than a dozen oil traders and shipping sources who told Reuters about storage in facilities that do not make their oil volumes public.

http://www.reuters.com/article/us-global-oil-stocks-analysis-idUSKCN18F0EO