Alaska Air Executive Says Incoming Yields For Continental U.S. Markets Have Sustained An Increase Of 20% Plus Year Over Year In Recent Weeks; Have Seen Refining Margins More Than Double And In Singapore, Refining Margins Spiked More Than 400% During Q1; Fuel Sourced From Singapore, Which Historically Has Been Consistently Lowest Cost Portion Of Our Supply, Became Most Expensive; In Just Past Seven Days, Fuel Prices Have Moved To As High As $5.15 Per Gallon And As Low As $4.45