ConocoPhillips is a balanced exploration and production company with plenty of upside potential. There are many different ways of approaching an investment in oil and gas. But one of the simplest is to target a company in the upstream oil and gas sector, whether that's an exploration and production (E&P) company, oil- field services and equipment provider, or integrated major. At a market cap just shy of $150 billion, ConocoPhillips (COP 0.09%) is the most valuable U.S.-based independent E&P. It's worth mor ...