Oil dropped to a six-month low in New York on concern that Greece will have to leave the euro, deepening Europe’s debt crunch and curbing fuel demand.

Futures fell as much as 1 percent after German Finance Minister Wolfgang Schaeuble said that financial market turmoil caused by the euro-zone crisis may last two more years. Prices are heading for the third straight weekly decline as U.S. consumer confidence dipped and American crude supplies climbed to the highest level since 1990.

Crude oil for June delivery fell to $91.60 a barrel, the lowest level since Nov.3 on the New York Mercantile Exchange. Prices have retreated 4.3 percent so far this week.

Brent oil for July settlement slipped 37 cents, or 0.3 percent, to $107.12 a barrel on the London-based ICE Futures Europe exchange. The European benchmark dropped to $106.40, the lowest level since Dec. 21.