( Oil ( ( is ( ( the ( biggest ( single source ) ) ) ( of ( ( the ( world 's ) ) energy ) ) ) ) . ) )
(ROOT (S (NP (NNP Oil)) (VP (VBZ is) (NP (NP (DT the) (JJS biggest) (JJ single) (NN source)) (PP (IN of) (NP (NP (DT the) (NN world) (POS 's)) (NN energy))))) (. .)))
Oil is the biggest single source of the world's energy.
(ROOT (S (NP (NNP Oil)) (VP (VBZ is) (NP (NP (DT the) (ADJP (RBS most) (RB commonly) (VBN used)) (NN source)) (PP (IN of) (NP (NP (NN energy)) (PP (IN in) (NP (DT the) (NN world))))))) (. .)))