Based on field observations and some discussions with U.S.
( Based ( on ( ( ( field observations ) and ) ( ( some discussions ) ( with U.S. ) ) ) ) )
(ROOT (PP (VBN Based) (PP (IN on) (NP (NP (NN field) (NNS observations)) (CC and) (NP (NP (DT some) (NNS discussions)) (PP (IN with) (NP (NNP U.S.))))))))
The field observations may have been faulty. 
( ( The ( field observations ) ) ( ( may ( have ( been faulty ) ) ) . ) )
(ROOT (S (NP (DT The) (NN field) (NNS observations)) (VP (MD may) (VP (VB have) (VP (VBN been) (ADJP (JJ faulty))))) (. .)))