Steep downward revisions to oil and gas reserves at the end of this year are likely to increase scrutiny of how energy companies tally future barrels – a process that has become more opaque with the rise of shale drilling. The revisions due in December will reflect a deep plunge in crude prices and should not come as a surprise for investors who have been pouring billions of dollars into U.S. oil companies betting that crude prices will recover. But investors may not fully appreciate other risks stemming from the wide variety of methods companies use to estimate and vet their reserves, or economically-recoverable oil and gas. Reserves have long underpinned company stock prices. Reserve growth is used at companies, including ConocoPhillips as a component of the chief executive’s compensation. Yet there is plenty of uncertainty in the industry as measuring unconventional resources such as shale oil […]