Airlines seek new ways to save on fuel as costs soar Fuel is an airline's biggest single expense. In 2008, the cost of jet fuel rocketed. Airlines tried to switch to newer generation aircraft, which have more fuel-efficient engines. Source: The New York Times, June 11, 2008 How does an increase in the price of fuel change an airline's total costs, average costs, and marginal cost? When the cost of fuel increases, average fixed cost _______ and average variable cost _______. A. does not change; increases B. increases; does not change C. decreases; increases D. increases; increases