Two big oil nations - Iraq and Venezuela - halted shipments Monday, sparking fears of a shortage. Iraq, which pumps 2.1 million to 2.4 million barrels a day, or about 3% of world supply, halted shipments to protest Israel's actions in the Palestinian territories. The embargo will last one month or until Israel withdraws, Iraq said. Israel began pulling out of some cities Tuesday morning. Meanwhile, a strike in Venezuela blocked oil from OPEC's No. 3 producer, costing the market 2.8 million barrels a day, or 4%. To make matters worse, a huge refinery shutdown in St. Croix, U.S. Virgin...