CF INDUSTRIES HOLDINGS, INC.  related to net operating loss carryforwards (NOLs) generated from business conducted with CF Industries, Inc. ’s pre-IPO owners.
These net operating loss carryforwards totaled $250 million, with expirations ranging from 2021 through 2023.
The income tax provision for the year ended December 31, 2005 includes a charge of $99.9 million to establish a 100% valuation allowance for the deferred tax asset related to these NOLs.
The valuation allowance is required because there is substantial uncertainty under existing tax law whether any tax benefits from this deferred tax asset will be realized since CF Industries, Inc.  is no longer a cooperative for federal income tax purposes.
In connection with the IPO, we entered into a net operating loss agreement with CF Industries, Inc. ’s pre-IPO owners (NOL Agreement) relating to the future treatment of the pre-IPO NOLs.
Under the NOL Agreement, if it is finally determined that CF Industries, Inc. ’s net operating loss carryforwards can be utilized subsequent to the IPO, we will pay to CF Industries, Inc. ’s pre-IPO owners an amount equal to the resulting federal and state income taxes actually saved.
CFL operates as a cooperative for Canadian income tax purposes and distributes all of its earnings as patronage dividends to its customers, including CF Industries, Inc.  For Canadian income tax purposes, CFL is permitted to deduct an amount equal to the patronage dividends it distributes to its customers, provided that certain requirements are met.
As a result, CFL records no income tax provision.12.
Cash and Cash Equivalents and Short-Term Investments Our cash and cash equivalents and short-term investments consist of the following:
## Table 0 ##
We invest our excess cash balances in several types of securities, including notes and bonds issued by governmental entities or corporations, and money market funds.
Securities issued by governmental agencies include those issued directly by the U. S.  government, those issued by state, local or other governmental entities, and those guaranteed by entities affiliated with governmental entities.
We had short-term investments of $494.5 million as of December 31, 2007 and $300.2 million as of December 31, 2006.
In 2007, our short-term investments generally were available-for-sale tax exempt auction rate securities.
Auction rate securities primarily are debt instruments with long-term maturities for which interest rates are reset periodically through an auction process, which typically occurs every 7 to 35 days.
The auction process results in the interest rate being reset on the underlying securities until the next reset or auction date.
This date is also referred to as the remarketing date, since the holder of the instrument can decide at each auction date to continue to hold the security or allow others to bid for it resulting in liquidation of the original holder’s position.
Parties bid for these instruments and the lowest interest rate that places all of the securities offered for auction becomes the interest rate earned until the next auction date.
A failed auction occurs when there are insufficient bids for the number of
CF INDUSTRIES HOLDINGS, INC.  30.
Stock-Based Compensation 2009 Equity and Incentive Plan On April 21, 2009, our shareholders approved the CF Industries Holdings, Inc.  2009 Equity and Incentive Plan (Plan), which replaced the CF Industries Holdings, Inc.  2005 Equity and Incentive Plan (2005 Plan).
Under the Plan, we may grant incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock, restricted stock units, performance awards (payable in cash or stock) and other stock-based awards to our officers, employees, consultants and independent contractors (including non-employee directors).
The purpose of the Plan is to provide an incentive for our employees, officers, consultants and non-employee directors that is aligned with the interests of our stockholders.
Share Reserve and Individual Award Limits The maximum number of shares reserved for the grant of awards under the Plan is the sum of (i) 3.9 million and (ii) the number of shares subject to outstanding awards under the 2005 Plan to the extent such awards terminate or expire without delivery of shares.
For purposes of determining the number of shares of stock available for grant under the Plan, each option or stock appreciation right is counted against the reserve as one share.
Each share of stock granted, other than an option or a stock appreciation right, is counted against the reserve as 1.61 shares.
If any outstanding award expires for any reason or is settled in cash, any unissued shares subject to the award will again be available for issuance under the Plan.
Shares tendered in payment of the exercise price of an option and shares withheld by the Company or otherwise received by the Company to satisfy tax withholding obligations are not available for future grant under the Plan.
At December 31, 2010, we had 3.4 million shares available for future awards under the Plan.
The Plan provides that no more than 1.0 million underlying shares may be granted to a participant in any one calendar year.
Stock Options Under the Plan, we granted to plan participants nonqualified options to purchase shares of our common stock.
The exercise price of these options is equal to the market price of our common stock on the date of grant.
The contractual life of the options is ten years and generally one-third of the options vest on each of the first three anniversaries of the date of grant.
The fair value of each stock option award is estimated using the Black-Scholes option valuation model.
Key assumptions used and resulting grant date fair values are shown in the following table.
## Table 1 ##
The expected volatility of our stock options is based on the combination of the historical volatility of our stock and implied volatilities of exchange traded options on our stock.
The expected term of options is estimated based on our historical exercise experience, post vesting employment termination behavior and the contractual term.
The risk-free interest rate is based on the U. S.  Treasury Strip yield curve in effect at the time of grant for the expected term of the options.
CF INDUSTRIES HOLDINGS, INC.  55 UAN Segment Our UAN segment produces urea ammonium nitrate solution (UAN).
UAN, a liquid fertilizer product with a nitrogen content that typically ranges from 28% to 32%, is produced by combining urea and ammonium nitrate.
UAN is produced at our nitrogen complexes in Courtright, Ontario; Donaldsonville, Louisiana; Port Neal, Iowa; Verdigris, Oklahoma; Woodward, Oklahoma; and Yazoo City, Mississippi.
The following table presents summary operating data for our UAN segmen
## Table 2 ##
(1) UAN represents between 28% and 32% of nitrogen content, depending on the concentration specified by the customer.
Nutrient tons represent the tons of nitrogen within the product tons.
Year Ended December 31, 2015 Compared to Year Ended December 31, 2014 Net Sales.
Net sales in the UAN segment decreased $190.1 million, or 11%, in 2015 due primarily to an 8% decrease in average selling prices and a 4% decrease in sales volume.
Average selling prices decreased to $252 per ton in 2015 compared to $274 in 2014.
The decline in UAN average selling prices was due to excess global supply availability weighing on global nitrogen fertilizer selling prices.
Sales volume was lower as customers delayed purchases in the declining pricing environment.
Cost of Sales.
Cost of sales per ton in our UAN segment averaged $162 in 2015, a 1% decrease from the average of $164 per ton in 2014.
The decrease was due primarily to lower realized natural gas costs partly offset by the impact of higher unrealized net mark-to-market losses on natural gas derivatives in 2015 compared to 2014.
Year Ended December 31, 2014 Compared to Year Ended December 31, 2013 Net Sales.
Net sales in the UAN segment decreased by $265.3 million, or 14%, due to a 10% decrease in average selling prices and a 5% decrease in sales volume.
The decrease in UAN prices and volume was due primarily to the combination of customer preferences for attractively priced ammonia during the extended spring ammonia application season and lower production.
Sales volume was negatively impacted by unplanned outages at the Woodward, Oklahoma nitrogen complex for maintenance and repairs of certain critical equipment.
Cost of Sales.
Cost of sales per ton in our UAN segment averaged $164 in 2014, a 17% increase over the $140 per ton in 2013 due primarily to increased natural gas costs which increased 16%, plus the impact of mark-to-market on natural gas derivatives which increased UAN segment gas costs by $49.3 million compared to 2013.
Entergy Arkansas, Inc.  Management's Financial Discussion and Analysis 251 Gross operating revenues and fuel and purchased power expenses Gross operating revenues increased primarily due to: x an increase of $114 million in gross wholesale revenue due to an increase in the average price of energy available for resale sales and an increase in sales to affiliated customers; x an increase of $106.1 million in production cost allocation rider revenues which became effective in July 2007 as a result of the System Agreement proceedings.
As a result of the System Agreement proceedings, Entergy Arkansas also has a corresponding increase in deferred fuel expense for payments to other Entergy system companies such that there is no effect on net income.
Entergy Arkansas makes payments over a seven-month period but collections from customers occur over a twelve-month period.
The production cost allocation rider is discussed in Note 2 to the financial statements and the System Agreement proceedings are referenced below under "Federal Regulation"; and x an increase of $58.9 million in fuel cost recovery revenues due to changes in the energy cost recovery rider effective April 2008 and September 2008, partially offset by decreased usage.
The energy cost recovery rider filings are discussed in Note 2 to the financial statements.
The increase was partially offset by a decrease of $14.6 million related to volume/weather, as discussed above.
Fuel and purchased power expenses increased primarily due to an increase of $106.1 million in deferred System Agreement payments, as discussed above and an increase in the average market price of purchased power.2007 Compared to 2006 Net revenue consists of operating revenues net of: 1) fuel, fuel-related expenses, and gas purchased for resale, 2) purchased power expenses, and 3) other regulatory credits.
Following is an analysis of the change in net revenue comparing 2007 to 2006.
## Table 3 ##
The net wholesale revenue variance is primarily due to lower wholesale revenues in the third quarter 2006 due to an October 2006 FERC order requiring Entergy Arkansas to make a refund to a coal plant co-owner resulting from a contract dispute, in addition to re-pricing revisions, retroactive to 2003, of $5.9 million of purchased power agreements among Entergy system companies as directed by the FERC.
The transmission revenue variance is primarily due to higher rates and the addition of new transmission customers in late 2006.
The deferred fuel cost revisions variance is primarily due to the 2006 energy cost recovery true-up, made in the first quarter 2007, which increased net revenue by $6.6 million.
Gross operating revenue and fuel and purchased power expenses Gross operating revenues decreased primarily due to a decrease of $173.1 million in fuel cost recovery revenues due to a decrease in the energy cost recovery rider effective April 2007.
The energy cost recovery rider is discussed in Note 2 to the financial statements.
The decrease was partially offset by production cost allocation rider revenues of $124.1 million that became effective in July 2007 as a result of the System Agreement proceedings.
As

Tables referenced above, in order (Table 0 first):
<table><tr><td> </td><td colspan="2"> December 31,</td></tr><tr><td> </td><td> 2007</td><td> 2006</td></tr><tr><td> </td><td colspan="2"> (in millions)  </td></tr><tr><td>Cash</td><td>$9.1</td><td>$6.5</td></tr><tr><td>Cash equivalents:</td><td></td><td></td></tr><tr><td>Federal government obligations</td><td>325.4</td><td>—</td></tr><tr><td>Other debt securities</td><td>32.0</td><td>18.9</td></tr><tr><td>Total cash and cash equivalents</td><td>$366.5</td><td>$25.4</td></tr><tr><td>Short-term investments:</td><td></td><td></td></tr><tr><td>State and local government obligations</td><td>$494.5</td><td>$277.7</td></tr><tr><td>Other debt securities</td><td>—</td><td>22.5</td></tr><tr><td>Total short-term investments</td><td>$494.5</td><td>$300.2</td></tr></table>
<table><tr><td> </td><td> 2010</td><td> 2009</td><td> 2008</td></tr><tr><td>Assumptions:</td><td></td><td></td><td></td></tr><tr><td>Weighted-average expected volatility</td><td>52%</td><td>54%</td><td>58%</td></tr><tr><td>Expected term of stock options</td><td>5-6 Years</td><td>4-5 Years</td><td>5 Years</td></tr><tr><td>Risk-free interest rate</td><td>1.5-2.0%</td><td>2.3-2.9%</td><td>1.5%-3.3%</td></tr><tr><td>Weighted-average expected dividend yield</td><td>0.5%</td><td>0.5%</td><td>0.3%</td></tr><tr><td>Weighted-average grant date fair value per share of options granted</td><td>$35.04</td><td>$37.24</td><td>$61.59</td></tr></table>
<table><tr><td></td><td colspan="7">Twelve months ended December 31,</td></tr><tr><td></td><td>2015</td><td>2014</td><td>2013</td><td colspan="2">2015 v. 2014</td><td colspan="2">2014 v. 2013</td></tr><tr><td></td><td colspan="7">(in millions, except as noted)</td></tr><tr><td>Net sales</td><td>$1,479.7</td><td>$1,669.8</td><td>$1,935.1</td><td>$-190.1</td><td>-11%</td><td>$-265.3</td><td>-14%</td></tr><tr><td>Cost of sales</td><td>954.5</td><td>997.4</td><td>895.6</td><td>-42.9</td><td>-4%</td><td>101.8</td><td>11%</td></tr><tr><td>Gross margin</td><td>$525.2</td><td>$672.4</td><td>$1,039.5</td><td>$-147.2</td><td>-22%</td><td>$-367.1</td><td>-35%</td></tr><tr><td>Gross margin percentage</td><td>35.5%</td><td>40.3%</td><td>53.7%</td><td>-4.8%</td><td></td><td>-13.4%</td><td></td></tr><tr><td>Sales volume by product tons (000s)</td><td>5,865</td><td>6,092</td><td>6,383</td><td>-227</td><td>-4%</td><td>-291</td><td>-5%</td></tr><tr><td>Sales volume by nutrient tons (000s)<sup>(1)</sup></td><td>1,854</td><td>1,925</td><td>2,015</td><td>-71</td><td>-4%</td><td>-90</td><td>-4%</td></tr><tr><td>Average selling price per product ton</td><td>$252</td><td>$274</td><td>$303</td><td>$-22</td><td>-8%</td><td>$-29</td><td>-10%</td></tr><tr><td>Average selling price per nutrient ton<sup>-1</sup></td><td>$798</td><td>$867</td><td>$960</td><td>$-69</td><td>-8%</td><td>$-93</td><td>-10%</td></tr><tr><td>Gross margin per product ton</td><td>$90</td><td>$110</td><td>$163</td><td>$-20</td><td>-18%</td><td>$-53</td><td>-33%</td></tr><tr><td>Gross margin per nutrient ton<sup>-1</sup></td><td>$283</td><td>$349</td><td>$516</td><td>$-66</td><td>-19%</td><td>$-167</td><td>-32%</td></tr><tr><td>Depreciation and amortization</td><td>$191.6</td><td>$179.3</td><td>$172.6</td><td>$12.3</td><td>7%</td><td>$6.7</td><td>4%</td></tr></table>
<table><tr><td></td><td>Amount (In Millions)</td></tr><tr><td>2006 net revenue</td><td>$1,074.5</td></tr><tr><td>Net wholesale revenue</td><td>13.2</td></tr><tr><td>Transmission revenue</td><td>11.8</td></tr><tr><td>Deferred fuel costs revisions</td><td>8.6</td></tr><tr><td>Other</td><td>2.5</td></tr><tr><td>2007 net revenue</td><td>$1,110.6</td></tr></table>

Question: What was the average of Cost of sales in 2015, 2014, and 2013? (in millions)
Answer: 949.167
Reasoning program: add(954.5,997.4), add(#0,895.6), divide(#1,const_3)