Last week was a tumultuous week for traders in oil markets as lingering doubts over the effectiveness that a production cut led by the nations of the Organization of Petroleum Exporting Countries (OPEC) was achieving the desired result of reducing global oil supply. The market has been saturated for over two years and some producers are seeking a return to what they consider to be a natural balance.

Oil futures both within the United States and abroad were fluctuating up and down last week with the emergence of doubts as to the effect which OPEC’s efforts to cut production were having on global supplies. In April a record 48 million barrels of crude oil were shipped across the ocean every day a jump of nearly 6% in less than 6 months since last December when the OPEC production cuts were implemented.

Of course this has not gone unnoticed by the markets. The entire Brent forward curve has been in a steady decline since OPEC began its cuts in January. Since January, the average monthly value of 24-month Brent curve is down 7% which is more than $4 a barrel to in the neighborhood of $54.15 a barrel.

Part of OPEC’s difficulty is that they control only approximately 1/3 of the world oil producing capacity and other producers who have no interest in cutting output have increased their exports accordingly. Most notable among these other exporters is the United States which joined the ranks of countries which export Petroleum for the first time in 40 years last year. Experts say the rise in U.S. shale is a major factor in the failure of OPEC’s efforts to stabilize market prices.

U.S. production has been rising by leaps and bounds jumping almost 10% in less than a year since the middle of 2016. Output stands at well over 9 million barrels per day which brings the country within striking distance of Saudi Arabia and Russia, the world’s top two oil producing countries. In an effort to prevent supplies from rising even further, some OPEC producers including Saudi Arabia are pushing to extend the pledged production cuts past the current June expiration.

Essential to determining the health of of oil markets is an accurate gauge of where current inventory levels stand. However, outside the United States with its excellent record keeping which continues to show inventories near capacity (the strategic reserve currently holds over 530 million barrels of oil, enough to supply the needs of the United States for 25 days), good data is difficult to come by.

Among the largest stumbling block preventing OPEC’s regulating of oil markets is the fact that the production cuts are voluntarily self enforced. This has led to allegations that members of OPEC have been selling oil above and beyond the agreed upon production levels to meet customer demand. Some OPEC members such as Nigeria have economies which are very much dependent upon oil (in 2016 2/3 of Nigerian government revenues came from oil sales).

Singapore which is an oil trading hub of Asia has shown falling inventories, yet it is still unclear if this is to to sales in response to strong demand or if this is due to transfers to create more room for anticipated supplies.