OPEC's crude oil production tumbled in August, snapping a two-month recovery, as output from group leader Saudi Arabia was curbed by threats to both of its export routes, according to a Bloomberg survey. Supplies from the Organization of the Petroleum Exporting Countries declined by 900,000 barrels a day last month to average 19.91 million a day. The drop in Saudi production was just over 1 million barrels, and marginally offset by gains in Iraq and Venezuela.