U.S. oil and natural gas producers are finding it difficult to source sufficiently skilled employees for petrochemical expansions that could be worth $100 billion. "The oil and gas industry has a missing generation. You have men and women who are in their 50s, and then from ... 1985 to the late 1990s, no one was graduating with petroleum engineering degrees and those sorts of things," said Carl Tricoli, global natural resources chief at Denham Capital Management.