Wood Group PSN chief executive Robin Watson said: "The acquisition of Elkhorn is an important part of our US shale strategy and will expand our service portfolio for our US onshore customers. Elkhorn's services and geographic presence are complementary to Wood Group PSN's existing shale business. Elkhorn, headed by chief executive Sean Sullivan, employs about 2,200 people and generated sales of about $250 million (£156m) last year.