Oil supply and demand doesn’t fully justify the 60% drop in prices between June and January as speculation also played a role. A rise in supply from outside the Organization at a time when demand for oil was weak was the main reason for the drop. Brent oil, benchmark for more than half of the world’s crude, tumbled from mid-June to a six-year low in January as U.S. output climbed to the highest level in more than four decades and OPEC members pumped more barrels.

“There was one other important factor that contributed to the downturn, especially as the price decline gained momentum,” OPEC said. “That was speculation.” OPEC’s interest is different from that of traders in the market as hedge funds and speculators need prices to fluctuate to make profits. The stability that OPEC and other energy stakeholders seek is of no help to them and severely limits their scope for gain.

OPEC oil production was little changed in April to 31.3 MMbpd as Saudi Arabia pumped 10 MMbpd, according to a Bloomberg survey. The organization’s ministers are scheduled to convene June 5 in Vienna to discuss the market and output targets.