ExxonMobil became the world's most valuable company by market capitalization in 2013 after years of oil-price strength.
ExxonMobil held the top global market-cap ranking in 2013 after overtaking Apple for a period. The ranking reflected the energy company's scale, profits, reserves, and investor expectations during an era of relatively strong crude-oil prices.
ExxonMobil was created in 1999 through the merger of Exxon and Mobil. Both companies trace their histories to the Standard Oil system established in the nineteenth century. The combined company became one of the world's largest integrated oil and gas businesses, spanning exploration, production, refining, chemicals, and fuel marketing.
Market-cap leadership can change without a company changing its physical size. In Exxon's case, technology-sector growth later pushed companies such as Apple and others above it. ExxonMobil is not the same entity as Chevron or the former Royal Dutch Shell; those are separate multinational energy companies.