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 more t ...