The second-largest U.S. oil company by market value spent "significant sums" and assigned some of its best scientists to evaluate more than 100 kinds of feedstock and 50 techniques for converting them into fuels without success, Chevron Chairman and Chief Executive Officer John Watson said during an address to the Economic Club of Minnesota in Minneapolis today. "The smartest minds in my company and others haven't yet cracked the code on pairing the right feedstock conversion technology and logistics in an economic and scalable package," Watson said.