Oil retreated below $71 a barrel as Saudi Arabia was said to offer extra crude to some customers, while the U.S. reportedly considered tapping emergency supplies, to offset output losses around the world. Futures in New York slid as much as 1 percent after falling 3.8 percent last week. Saudi Arabia offered additional cargoes of its Arab Extra Light crude to at least two buyers in Asia, people familiar with the matter said. Meanwhile the U.S., which is seeking to choke off crude exports from Iran, is said to be mulling releasing oil from its 660 million-barrel Strategic Petroleum Reserve. Prices are retreating from the three-year high hit last month as Saudi Arabia and its allies move to counteract supply losses elsewhere in the Organization of Petroleum Exporting Countries, such as the spiraling crisis in Venezuela, erratic flows in Libya and renewed U.S. sanctions on Iran. Oil is also slipping on concern that trade tensions between the U.S. and China will hurt demand.