The consumers pay for crude oil in dollars; hence, they always have to keep a steady reserve of dollars, thereby maintaining a high demand for the the currency. (oilprice.com)
Higher interest rates also impact demand for a currency, with higher - yielding currencies expected to appreciate against lower - yielding currencies, holding all else equal. (daytrading.com)
The yen and franc generally appreciate in value because the leveraged carry trades commonly funded by these currencies become unwound, not because of demand for these currencies themselves. (daytrading.com)