Saudi Arabia’s potential sale of shares in its state-owned oil giant raises the question of just how valuable that publicly listed company would be, with estimates of market valuations ranging into the trillions of dollars. Saudi Arabian Oil Co., better known as Saudi Aramco, produces more than 10% of the world’s oil supply every day and has built a large chain of refineries and petrochemical facilities to complement its exploration and production operations. Just using proved oil reserves as a benchmark for valuation, Saudi Aramco could be worth up to 20 times as much as Exxon Mobil Corp. XOM -2.02 % , the largest non-state-controlled publicly listed oil company with a market valuation of $317 billion. Saudi Aramco has 261 billion barrels of proved crude-oil reserves, according to its 2014 annual report, compared with less than 14 billion […]