Linhdtu,
Exxon has paid 'income' taxes in the U.S. for years, but it does pay somewhere around $6 to $8 Billion in U.S. duties.
Many of the undeveloped nations allow Exxonmobil to explore their countries but then basically tax them at rates up to 85% of the value of any extracted oil. Because these are classified as taxes and not royalties, Exxon is allowed to subtract them from its U.S. tax obligation.
The word 'taxes' in the oil business is somewhat all encompassing. As an example. between 2005-2009 Exxon had a total U.S. Net Income of $42 Billion yet paid U.S. taxes of $63 Billion.
Exxon itself advises that 26% of its revenue goes to taxes.