that the US imports about 4.5 billion (4.5 x 109) barrels of petroleum products per year (when averaged out over 10 years or so). Say that a barrel of crude oil yields 25 gallons of gas (a very rough estimate: it varies a lot depending on the source oil, the refinery, etc.) Driving 15000 miles, split between city and highway, will require (roughly) 950 gallons in a Suburban but only 325 gallons for a Prius. Say that the government introduces a plan to improve fuel economy in the US as much as if people were moving from Suburbans to Priuses. If 10% of all cars (i. e. 24 million of the 240 million out there in 2011) upgrade in this way, and each person drives 15000 miles per year as described above (and all gas comes from the amount imported), then by what percent would US imports of petroleum decrease