Quick Look: Companies like Continental Resources and Chesapeake Energy are two oil companies largely engaged in shale fracking, with Chesapeake forecasting more than 50% of its revenues coming from shale. Integrated oil companies that aren't completely dependent on shale will be a safer bet for investors.
http://www.sfgate.com/cgi-bin/article.cgi?f=/g/a/2012/01/26/investopedia70484.DTL