We could be on the verge of another major oil M&A boom like the historic one that brought Exxon and Mobil together. Mergers and acquisitions have the potential to shake up a market and send some stocks soaring, but the best industry plays aren’t all that obvious.

Horizontal drilling and fracking have opened new opportunities for investing in domestic energy, whether for pure-play explorers in developing shales, producers in mature areas, or service companies opening up the monster wells.