"Industry Insight" is a weekly series that examines sectors through what's known as the five forces of competition, which can help separate the winners from the losers. Come back every Monday at 6 a.m. to see which industries and companies will be put under review.As the price of gasoline soared to more than $4 a gallon last summer, Exxon Mobil ( XOM) executives took heat for booking $14.8 billion in quarterly earnings. The company, whose annual revenue exceeds the gross domestic product of countries including Belgium and Switzerland, is so profitable not only because of high energy prices, but due to competitive forces that act upon the oil and gas industry. In a way, Exxon Mobil can't help but be so successful. Thirty years ago, Michael Porter of the Harvard Business School in Boston famously described five forces that influence competition. The energy industry enjoys a mostly positive mix of these forces. As a result, investors should consider the oil and gas sector as an attractive long-term investment and disregard volatile energy prices. In addition to Exxon Mobil, Chevron ( CVX), BP ( BP) and ConocoPhillips ( COP) also are beneficiaries of these forces. To give an idea of the scope of the revenue that flows into these massive companies every quarter, consider Exxon Mobil's first-quarter revenue versus that of Proctor & Gamble ( PG), a consumer-products company that's similarly dominant. Exxon Mobil had sales of more than $64 billion, nearly four times that of Proctor & Gamble. In fact, it's even higher than Procter & Gamble and General Electric's ( GE) combined. Here are the five forces and how they affect the energy industry: Degree of rivalry: Rivalry is low. Since the product is a commodity, there is little need to create customer loyalty. So branding is out. People will pick the option that has the lowest cost. Some will even drive five miles to save a few cents a gallon. Thus, all players are essentially equal and the market price will be a function of supply and demand.