Although it is called "Guiding Principles" on their website, this will serve as their mission statement
Exxon Mobil Corporation is committed to being the world’s premier petroleum and petrochemical company. To that end, we must continuously achieve superior financial and operating results while adhering to the highest standards of business conduct. These unwavering expectations provide the foundation for our commitments to those with whom we interact:
Shareholders
We are committed to enhancing the long-term value of the investment dollars entrusted to us by our shareholders. By running the business profitably and responsibly we expect our shareholders to be rewarded with superior returns. This commitment drives the management of our company.
Customers
Success depends on our ability to consistently satisfy ever-changing customer preferences. We pledge to be innovative and responsive, while offering high quality products and services at competitive prices.
Employees
The exceptional quality of our workforce is a valuable competitive edge. To build on this advantage we will strive to hire and retain the most qualified people available and maximize their opportunities for success through training and development. We are committed to maintaining a safe work environment enriched by diversity and characterized by open communication, trust, and fair treatment.
Communities
We pledge to be a good corporate citizen in all the places we operate worldwide. We will maintain the highest ethical standards, obey all applicable laws and regulations, and respect local and national cultures. Above all other objectives, we are dedicated to running safe and environmentally responsible operations.
To be successful, ExxonMobil must be at the leading edge of competition in every aspect of our business. This requires that the Corporation’s substantial resources – financial, operational, technological, and human – be employed wisely and evaluated regularly.
While we maintain flexibility to adapt to changing conditions, the nature of our business requires a focused, long-term approach. We will consistently strive to improve efficiency and productivity through learning, sharing and implementing best practices. We will be disciplined and selective in evaluating the range of capital investment opportunities available to us. We will seek to develop proprietary technologies that provide a competitive edge.
We will achieve our goals by flawlessly executing our business plans and by strictly adhering to these guiding principles along with our more comprehensive Standards of Business Conduct.
Source: http://manonamission.blogspot.com/2005/04/exxon-mobils-xom-mission-statement.html