Rising oil and natural gas prices boosted third-quarter profits at Exxon Mobil Corp and Chevron Corp by about 50 percent, underscoring how reliant they remain on commodity markets for their financial futures than better technology or cost cuts.  Despite deep capital spending cuts and a refocusing on projects that can generate faster paybacks in recent years, the results on Friday showed the pair, neither of whom hedge oil output, are still at the mercy of price gyrations. Exxon and Chevron have pointed to aggressive plans for boosting low-cost U.S. shale production. But in recent quarters total output at both has atrophied and shale is unlikely to deliver a marked lift until the next decade, based […]