LONDON, UK — Although China accounts for only 8 percent of global oil consumption, well below America's 25 percent, it has accounted for as much as one-third of the increase in global oil demand over the past three years, almost twice as much as America, according to The Economist magazine. Citing information provided by Jonathan Anderson, the chief Asia economist at UBS in Hong Kong, China's oil demand will grow as incomes rise and more households can afford cars and energy-consuming household appliances. If UBS's forecasts of China's oil imports are correct, and if (a much bigger if) the relationship illustrated in the UBS data holds, oil prices could hit $70 a barrel within two years. If, on the other hand, China has a hard landing and its oil demand falls, expect prices to plunge.