Now, markets are weakening across Europe and Asia as buyers find themselves inundated with offers for cargo. In one of the most dramatic examples, Angolan crude — a grade that is typically snapped up by China — has been selling at the biggest discounts in more than a decade, at times changing hands at nearly $10 a barrel below the global Dated Brent benchmark. More broadly, traders say that Chinese refiners are offering oil cargoes for sale, in a stark reversal of normal flows.