The debate rages on: Is the United States witnessing a resurgence in its shale industry, or is the sector approaching a gradual decline? With high energy prices prompting fossil fuel giants to splurge on major acquisitions, the signals are mixed. ExxonMobil's $60 billion deal to purchase Pioneer Natural Resources and Chevron's $53 billion offer for Hess Corporation are two recent megadeals that have captured the industry's attention.