Saudi Arabia's oil minister told fellow OPEC members they must combat the U.S. shale oil boom, arguing against cutting crude output in order to depress prices and undermine the profitability of North American producers.
Simply over-production. They try to maintain a margin, a buffer to keep production where it should be without running out. When that buffer amount is too large it acts like a surplus and oil is a "supply and demand" product, so if supply appears too high then it is no longer "rare" but is instead plentiful. If you can create a "glut" then you can manipulate the price by making an "artificial" SHORTAGE. The REAL money to be made is in credit card charges. If gas doubles in price then credit card balances double and interest charges profits and other card fees double.
The Saudis are not slowing production to keep the price up. I don't know how long they can get away with it, because it is hurting the other OPEC companies, but I suspect their real motive is to knock the US back down a couple of pegs after we became the #1 oil exporting country last year.
OPEC is trying to conduct a price war against US shale oil producers. . If OPEC decides to stop this war and to cut production then the price of oil will go up again.