From staples.com:

Staples SoulSM reflects our commitment to corporate responsibility. It's a holistic approach to business that recognizes the close connection between our financial success and our desire to make a positive impact on our associates, communities, and the planet by joining together the following areas: diversity, the environment, our community, and ethics. It's how we do business—that's Staples Soul. Learn more about Staples Soul in our latest corporate responsibility report.

The part of Staple Soul that has to do with reducing fuel is explained in this text taken from a pdf on the Staple Soul page:

Mike Payette, Fleet Manager at Staples, is committed to improving fuel economy and reducing harmful emissions within our transportation fleet. In the fall of 2006, Mike and his team modified the engine electronic control modules on the delivery trucks in our fleet to limit the maximum driving speed to 60 mph, which has increased our fleet’s fuel economy, decreased greenhouse gas emissions and reduced maintenance costs. Based on initial testing, Staples expects to realize the following improvements in fuel economy:

• An increase from approximately 8.5 to 11 mpg for trucks delivering supplies
• An increase from approximately 8 to 10.5 mpg for trucks delivering furniture
• An overall improvement to fuel economy of 15 percent or more, which translates to an estimated fuel savings of more than 500,000 gallons of diesel annually.

That pretty sums it up.  Good job Staples. Your Staples Soul project is the DIFF!