Costs of energy, many believe, can only rise. Petrol prices rose to almost unprecedented heights in the U.S. in 2005, and despite a brief fall in early 2006, the trend is upward. The price of natural gas was a major political issue in Europe in the winter of 2005-6, and most commentators expect natural gas prices to rise further. The costs of aviation fuel are threatening the financial viability of many airline companies. Although some deserts command large reserves of oil and gas, most do not. Dearer energy will affect them all, but in different measure. In deserts, where the relation between the price of energy and that of water is close, more expensive energy will restrain many development schemes. The costs of solar and wind energy may be lower in deserts than in some other places, but even so, they do not yet compete well with fossil fuels, except in a few sites, and their cost-trajectory is uncertain, especially if cheap fossil energy is not available to build the necessary facilities. The costs of travel seem bound to rise, so that tourism may suffer (among many other things), although rising travel costs are claimed not yet to have had an effect in the U.S.