With the price of oil –– and air fuel –– continuing to climb higher than the jets it flies, Delta Air Lines raised its most expensive fares last week by $100. Continental, United, and Northwest Airlines, and American Airlines all quickly followed suit. Delta boosted its maximum fare to $599, up frm $499, for one-way, walk-up fares for economy class and to $699 for first class. This came a half-year after it had announced a ticket price overhaul to attract more business travelers.