“Big oil” is really a misnomer. It may not be for long. The largest energy company that investors can easily own is Exxon Mobil . XOM -2.02 % It is by most standards massive, having rivaled Apple for the global market-value crown before the latest commodity swoon. But its proven reserves of 25 billion oil-equivalent barrels pale in comparison with Saudi Aramco, which is more than 10 times its size on that measure and pumps over one-tenth of the world’s crude. News last week that the Saudi government is considering an initial public offering for the producer set off speculation about the world’s first trillion-dollar-plus company by market value and put dollar signs in the eyes of some bankers and energy investors . While the deal may never happen and could well be restricted to domestic buyers if it does, how should investors react if it materializes? Any trepidation […]