Major airlines have followed the lead of Southwest Airlines and JetBlue Airways in raising round-trip fares by $10 this week. United Airlines, Delta Air Lines, American Airlines and US Airways announced on Thursday that they had also raised airfares. The jet-fuel bill for airlines has risen in tandem with crude oil prices. "This week the spot price for Gulf Coast jet fuel was 12.1% higher than a year ago," this feature says. In 2011, airlines raised base airfares around a dozen times.