Summary: U.S. markets ended Thursday's session in the red, but each lost no more than 1%. Oil was a big mover in the commodities space. Crude oil prices reached their highest level since September 2013. Oil investors are concerned because of the escalating tension in Iraq. Sunni Islamist militants surrounded the country's largest refinery in the Northern city of Baiji on Thursday. Repairs to some of the pipelines in Baiji are reportedly being halted. The escalation of violence in Iraq poses a big threat to the country's oil exports. Iraq is the second largest OPEC producer and the Baiji refinery produces 310,000 barrels a day. One sector moving lower on Thursday because of the threat of a decline in oil supplies is airlines. Delta Air Lines finished Thursday's session down 6% and Southwest Airlines ended down nearly 5%. The Dow Jones Transportation Average lost 2%. On the economic front, the number of people who applied for jobless benefits last week increased 4,000 to 317,000, that's more than what economists had expected. The 4-week average, which a less volatile measure, also increased to more than 315,000.
