, ▁and ▁by ▁ 1 8 8 5 ▁it ▁had ▁e cli ps ed ▁wood ▁as ▁the ▁nation ' s ▁primary ▁energy ▁source . ▁ ▁Co al ▁remained ▁dominant ▁for ▁the ▁next ▁seven ▁dec ades , ▁but ▁by ▁ 1 9 5 0 , ▁it ▁was ▁sur pass ed ▁in ▁turn ▁by ▁both ▁pet role um ▁and ▁natural ▁gas . ▁The ▁ 1 9 7 3 ▁oil ▁embargo ▁precip itated ▁an ▁energy ▁crisis ▁in ▁the ▁United ▁States . ▁In ▁ 2 0 0 7 , ▁coal ▁consumption ▁was ▁the ▁highest ▁it ▁has ▁ever ▁been , ▁with ▁it ▁mostly ▁being ▁used ▁to ▁generate ▁electric ity . ▁Natural ▁gas ▁has ▁replaced ▁coal ▁as ▁the ▁preferred ▁source ▁of ▁he ating ▁in ▁homes , ▁business es , ▁and ▁industrial ▁furn aces , ▁which ▁burn s ▁cleaner ▁and ▁is ▁easier ▁to ▁transport . ▁ ▁Although ▁total ▁energy ▁use ▁increased ▁by ▁approximately ▁a ▁factor ▁of ▁ 5 0 ▁between ▁ 1 8 5 0 ▁and ▁ 2 0 0 0 , ▁energy ▁use ▁per ▁cap ita ▁increased ▁only ▁by ▁a ▁factor ▁of ▁four . ▁As ▁of ▁ 2 0 0 9 , ▁United ▁States ▁per - cap ita ▁energy ▁use ▁had ▁decl ined ▁to ▁, ▁ 1 2 % ▁less ▁than ▁ 2 0 0 0 , ▁and ▁in ▁ 2 0 1 0 , ▁to ▁levels ▁not ▁seen ▁since ▁the ▁ 1 9 6 0 s . ▁At ▁the ▁beginning ▁of ▁the ▁ 2 0 th ▁century , ▁pet role um ▁was ▁a ▁minor ▁resource ▁used ▁to ▁manufact