Everything gets more expensive because of inflation. Inflation is a currency losing value, mostly because the money supply has been expanded. If there is more oil and the demand for oil stays the same the value of oil decreases, if there is less oil and the demand for oil stays the same the value of oil increases. The same thing happens with everything, including currencies. If the supply of dollar is drastically increased from $16trillion to $21trillion in a short timespan then the value of dollars relative to everything should drop. And it has started to drop, we just don't know where it will settle.