2022 fuel prices 2013 crude oil prices increased at a steady rate in 2007 , rising from a low of $ 56.58 per barrel in january to close at nearly $ 96.00 per barrel at the end of december . our 2007 average fuel price increased by 9% ( 9 % ) and added $ 242 million of operating expenses compared to 2006 . our fuel surcharge programs are designed to help offset the impact of higher fuel prices . in addition , our fuel conservation efforts allowed us to improve our consumption rate by 2% ( 2 % ) . locomotive simulator training , operating practices , and technology all contributed to this improvement , saving approximately 21 million gallons of fuel in 2007 . 2022 free cash flow 2013 cash generated by operating activities totaled a record $ 3.3 billion , yielding free cash flow of $ 487 million in 2007 . free cash flow is defined as cash provided by operating activities , less cash used in investing activities and dividends paid . free cash flow is not considered a financial measure under accounting principles generally accepted in the united states ( gaap ) by sec regulation g and item 10 of sec regulation s-k . we believe free cash flow is important in evaluating our financial performance and measures our ability to generate cash without additional external financings . free cash flow should be considered in addition to , rather than as a substitute for , cash provided by operating activities . the following table reconciles cash provided by operating activities ( gaap measure ) to free cash flow ( non-gaap measure ) : millions of dollars 2007 2006 2005 .
what was the percentage increase in the cash provided by operating activities from 2006 to 2007
2008 outlook 2022 safety 2013 operating a safe railroad benefits our employees , our customers , our shareholders , and the public . we will continue using a multi-faceted approach to safety , utilizing technology , risk assessment , quality control , and training for , and engaging with our employees . we plan to implement total safety culture ( tsc ) throughout our operations . tsc , an employee-focused initiative that has helped improve safety , is a process designed to establish , maintain , and promote safety among co-workers . with respect to public safety , we will continue our efforts to maintain , upgrade , and close crossings , install video cameras on locomotives , and educate the public about crossing safety through various internal and industry programs , along with other activities . 2022 commodity revenue 2013 despite uncertainty regarding the u.s . economy , we expect record revenue in 2008 based on current economic indicators , forecasted demand , improved customer service , and additional opportunities to reprice certain of our business . yield increases and fuel surcharges will be the primary drivers of commodity revenue growth in 2008 . we expect that overall volume will fall within a range of 1% ( 1 % ) higher to 1% ( 1 % ) lower than 2007 , with continued softness in some market sectors . 2022 transportation plan 2013 in 2008 , we will continue to evaluate traffic flows and network logistic patterns to identify additional opportunities to simplify operations and improve network efficiency and asset utilization . we plan to maintain adequate manpower and locomotives , improve productivity using industrial engineering techniques , and improve our operating margins . 2022 fuel prices 2013 fuel prices should remain volatile , with crude oil prices and conversion and regional spreads fluctuating throughout the year . on average , we expect fuel prices to increase 15% ( 15 % ) to 20% ( 20 % ) above the average price in 2007 . to reduce the impact of fuel price on earnings , we will continue to seek recovery from our customers through our fuel surcharge programs and expand our fuel conservation efforts. .