{"pre_text": ["2022 lower 2008 storage margins related to storage risk management positions and the impact of changes in natural gas prices on these positions ; and 2022 fewer opportunities to optimize storage capacity due to the significant decline in natural gas prices in the second half of 2008 ; o a decrease of $ 9.7 million in physical storage margins due to a lower of cost or market write-down on natural gas inventory ; and o a decrease of $ 2.1 million due to colder than anticipated weather and market conditions that increased the supply cost of managing our peaking and load-following services and provided fewer opportunities to increase margins through optimization activities , primarily in the first quarter of 2008 ; partially offset by o an increase of $ 15.8 million from changes in the unrealized fair value of derivative instruments associated with storage and marketing activities and improved marketing margins , which benefited from price movements and optimization activities .", "operating costs decreased primarily due to lower employee-related costs and depreciation expense .", "2007 vs .", "2006 - net margin decreased primarily due to : 2022 a decrease of $ 22.0 million in transportation margins , net of hedging activities , associated with changes in the unrealized fair value of derivative instruments and the impact of a force majeure event on the cheyenne plains gas pipeline , as more fully described below ; 2022 a decrease of $ 5.0 million in retail activities from lower physical margins due to market conditions and increased competition ; 2022 a decrease of $ 4.3 million in financial trading margins that was partially offset by 2022 an increase of $ 4.9 million in storage and marketing margins , net of hedging activities , related to : o an increase in physical storage margins , net of hedging activity , due to higher realized seasonal storage spreads and optimization activities ; partially offset by o a decrease in marketing margins ; and o a net increase in the cost associated with managing our peaking and load following services , slightly offset by higher demand fees collected for these services .", "in september 2007 , a portion of the volume contracted under our firm transportation agreement with cheyenne plains gas pipeline company was curtailed due to a fire at a cheyenne plains pipeline compressor station .", "the fire damaged a significant amount of instrumentation and electrical wiring , causing cheyenne plains gas pipeline company to declare a force majeure event on the pipeline .", "this firm commitment was hedged in accordance with statement 133 .", "the discontinuance of fair value hedge accounting on the portion of the firm commitment that was impacted by the force majeure event resulted in a loss of approximately $ 5.5 million that was recognized in the third quarter of 2007 , of which $ 2.4 million of insurance proceeds were recovered and recognized in the first quarter of 2008 .", "cheyenne plains gas pipeline company resumed full operations in november 2007 .", "operating costs decreased primarily due to decreased legal and employee-related costs , and reduced ad-valorem tax expense .", "selected operating information - the following table sets forth certain selected operating information for our energy services segment for the periods indicated. ."], "post_text": ["our natural gas in storage at december 31 , 2008 , was 81.9 bcf , compared with 66.7 bcf at december 31 , 2007 .", "at december 31 , 2008 , our total natural gas storage capacity under lease was 91 bcf , compared with 96 bcf at december 31 , natural gas volumes marketed decreased slightly during 2008 , compared with 2007 , due to increased injections in the third quarter of 2008 .", "in addition , demand for natural gas was impacted by weather-related events in the third quarter of 2008 , including a 15 percent decrease in cooling degree-days and demand disruption caused by hurricane ike. ."], "table": [["operating information", "years ended december 31 , 2008", "years ended december 31 , 2007", "years ended december 31 , 2006"], ["natural gas marketed ( bcf )", "1160", "1191", "1132"], ["natural gas gross margin ( $ /mcf )", "$ 0.07", "$ 0.19", "$ 0.22"], ["physically settled volumes ( bcf )", "2359", "2370", "2288"]], "table_ori": [["", "Years Ended December 31,"], ["Operating Information", "2008", "2007", "2006"], ["Natural gas marketed(Bcf)", "1,160", "1,191", "1,132"], ["Natural gas gross margin($/Mcf)", "$0.07", "$0.19", "$0.22"], ["Physically settled volumes(Bcf)", "2,359", "2,370", "2,288"]]}

Question: what was the percentage change in natural gas gross margin ( $ /mcf ) between 2007 and 2008?
Evidence:
table_2: operating information the natural gas gross margin ( $ /mcf ) of years ended december 31 , 2008 is $ 0.07 ; the natural gas gross margin ( $ /mcf ) of years ended december 31 , 2007 is $ 0.19 ; the natural gas gross margin ( $ /mcf ) of years ended december 31 , 2006 is $ 0.22 ;
Program: subtract(0.07, 0.19), divide(#0, 0.19)
Answer:
str_answer: -63%
exe_answer: -0.63158