As of December 31, 2014 and 2013, our liabilities associated with unrecognized tax benefits are not material.
We and our subsidiaries file income tax returns in the U. S.  federal jurisdiction and various foreign jurisdictions.
With few exceptions, the statute of limitations is no longer open for U. S.  federal or non-U.
S.  income tax examinations for the years before 2011, other than with respect to refunds.
U. S.  income taxes and foreign withholding taxes have not been provided on earnings of $291 million, $222 million and $211 million that have not been distributed by our non-U.
S.  companies as of December 31, 2014, 2013 and 2012.
Our intention is to permanently reinvest these earnings, thereby indefinitely postponing their remittance to the U. S.  If these earnings had been remitted, we estimate that the additional income taxes after foreign tax credits would have been approximately $55 million in 2014, $50 million in 2013 and $45 million in 2012.
Our federal and foreign income tax payments, net of refunds received, were $1.5 billion in 2014, $787 million in 2013 and $890 million in 2012.
Our 2014 and 2013 net payments reflect a $200 million and $550 million refund from the IRS primarily attributable to our tax-deductible discretionary pension contributions during the fourth quarters of 2013 and 2012, and our 2012 net payments reflect a $153 million refund from the IRS related to a 2011 capital loss carryback.
Note 8 – Debt Our long-term debt consisted of the following (in millions):
## Table 0 ##
In August 2014, we entered into a new $1.5 billion revolving credit facility with a syndicate of banks and concurrently terminated our existing $1.5 billion revolving credit facility which was scheduled to expire in August 2016.
The new credit facility expires August 2019 and we may request and the banks may grant, at their discretion, an increase to the new credit facility of up to an additional $500 million.
The credit facility also includes a sublimit of up to $300 million available for the issuance of letters of credit.
There were no borrowings outstanding under the new facility through December 31, 2014.
Borrowings under the new credit facility would be unsecured and bear interest at rates based, at our option, on a Eurodollar Rate or a Base Rate, as defined in the new credit facility.
Each bank’s obligation to make loans under the credit facility is subject to, among other things, our compliance with various representations, warranties and covenants, including covenants limiting our ability and certain of our subsidiaries’ ability to encumber assets and a covenant not to exceed a maximum leverage ratio, as defined in the credit facility.
The leverage ratio covenant excludes the adjustments recognized in stockholders’ equity related to postretirement benefit plans.
As of December 31, 2014, we were in compliance with all covenants contained in the credit facility, as well as in our debt agreements.
We have agreements in place with financial institutions to provide for the issuance of commercial paper.
There were no commercial paper borrowings outstanding during 2014 or 2013.
If we were to issue commercial paper, the borrowings would be supported by the credit facility.
In April 2013, we repaid $150 million of long-term notes with a fixed interest rate of 7.38% due to their scheduled maturities.
During the next five years, we have scheduled long-term debt maturities of $952 million due in 2016 and $900 million due in 2019.
Interest payments were $326 million in 2014, $340 million in 2013 and $378 million in 2012.
All of our existing unsecured and unsubordinated indebtedness rank equally in right of payment.
Note 9 – Postretirement Plans Defined Benefit Pension Plans and Retiree Medical and Life Insurance Plans Many of our employees are covered by qualified defined benefit pension plans and we provide certain health care and life insurance benefits to eligible retirees (collectively, postretirement benefit plans).
We also sponsor nonqualified defined benefit pension plans to provide for benefits in excess of qualified plan limits.
Non-union represented employees hired after December 2005 do not participate in our qualified defined benefit pension plans, but are eligible to participate in a qualified
Noble Energy, Inc.
Supplemental Oil and Gas Information (Unaudited) 115 Proved Gas Reserves (Unaudited) The following reserves schedule was developed by our qualified petroleum engineers and sets forth the changes in estimated quantities of proved natural gas reserves:
## Table 1 ##
(1) Other International includes the North Sea, Ecuador (at December 31, 2009 and 2008), and China.
See Note 3.
Acquisitions and Divestitures and Note 4.
Asset Impairments.
(2) The 2008 negative revisions in the US are primarily due to lower year-end prices (109 Bcf), as well as additional natural gas volumes being reflected in the proved oil reserves table as NGLs.
The 2009 negative revisions in the US are primarily due to lower year-end prices (224 Bcf), reclassifications of PUDs to probable reserves as a result of the SEC’s new five year development rule (75 Bcf), and increased lease operating expense and various well performance issues (98 Bcf).
The 2010 US revisions are a combination of increases from higher natural gas prices, which were more than offset by gas shrinkage from additional NGLs booked in Wattenberg and the reclassification of 85 Bcf of PUDs to probable reserves, primarily in Wattenberg, as a result of the SEC's five year development rule.
Equatorial Guinea’s positive revisions in 2008, 2009 and 2010 are primarily due to additional production allowances related to LNG sales.
Israel revisions in 2010 reflect a change in the likelihood that the Noa Field will be developed.
(3) The 2008 increase in US proved reserves includes 106 Bcf in Wattenberg and 173 Bcf in the Rocky Mountain area, primarily in the Piceance Basin and Niobrara formation, primarily due to infill drilling activities.
The remaining increase is due to other development programs.
The 2009 increase in US proved reserves is primarily due to ongoing low-risk development programs onshore in Wattenberg, the Rocky Mountain area, and East Texas.
The 2010 increase in US proved reserves is due to continuing development of onshore assets, primarily in the Central DJ Basin, Piceance Basin, and East Texas.
The 2010 increase in Israel is due to the recording of initial reserves at the Tamar development.
(4) The increase relates to our Mid-Continent acquisition in 2008 and our Central DJ Basin asset acquisition in 2010.
See Note 3.
Acquisitions and Divestitures.
(5) We sold non-core, mature onshore US assets in the Mid-Continent and Illinois Basin in 2010.
Other International sales in 2010 include 160 Bcf due to the termination of the Block 3 PSC by the Ecuadorian government.
As of December 31, 2015, approximately $457 million of our $1.0 billion cash and cash equivalents was held by foreign subsidiaries.
Non-Core Asset Sales and Other Divestitures During 2015, we generated $151 million cash from divestitures of non-core onshore US assets.
More recently, in January 2016, we received over $190 million cash from the close of our Cyprus farmout and sale of Tanin and Karish discoveries.
Debt Refinancing Also in January 2016, we completed a series of transactions, consisting of a new term loan and cash tender offers for certain outstanding notes, which we expect will collectively enhance our financial flexibility and result in future interest expense savings.
See Financing Activities, below.
Dividend Reduction On January 26, 2016, our Board of Directors adjusted the quarterly dividend to 10 cents per common share, which represents a reduction of 8 cents from fourth quarter 2015, aligns the dividend yield with historical levels, and further enhances our liquidity.
Available Liquidity Year-end liquidity was as follows:
## Table 2 ##
(1) See Credit Facility, below.
(2) Total debt includes capital lease and other obligations and excludes unamortized debt discount, premium, and issuance costs.
(3) We define our ratio of debt-to-book capital as total debt (which includes long-term debt excluding unamortized premium/discount and unamortized debt issuance costs, the current portion of long-term debt, and short-term borrowings) divided by the sum of total debt plus shareholders’ equity.
Current Activity - Impact on Liquidity Despite a 42% reduction in capital spending, excluding the Rosetta Merger, in 2015 versus 2014, and significant decreases in operating and general and administrative expenses, continually falling commodity prices resulted in capital expenditures exceeding operating cash flows for fiscal year 2015.
For 2016, our comprehensive effort to spend within cash flow includes both a substantially reduced and flexible capital program, as well as a dividend adjustment.
In January 2016, our Board of Directors adjusted the Company's quarterly cash dividend to 10 cents per common share, which represents a reduction of 8 cents from fourth quarter 2015 and aligns the dividend yield with historical levels.
The extent to which capital investment could exceed operating cash flows in the future depends on the pace of future development activities, timing of future development project sanction, the results of our exploration activities, and new business opportunities, as well as external factors such as commodity prices, among others.
Despite the low commodity price environment, we believe our financial capacity, coupled with our increasingly diversified portfolio, provides us with flexibility in our investment decisions including execution of major development projects as well as exploration activity in the current commodity price environment.
See Operating Outlook – 2016 Capital Investment Program, above.
To support our investment program, we expect that production resulting from our core onshore US development programs, including production from our Texas assets, combined with new production from the Big Bend and Dantzler development projects, which have recently begun producing, and from the Gunflint development, which is expected to begin producing in 2016, as well as increased peak deliverability resulting from the Tamar compression project, and presuming no significant further deterioration of prices, will result in an increase in cash flows which will be available to meet a portion of future capital commitments in 2016 and subsequent years.
We are currently evaluating potential development and/or financing scenarios for significant discoveries, including the Leviathan development project offshore Eastern Mediterranean.
The magnitude of certain discoveries presents technical and

Tables referenced above, in order (Table 0 first):
<table><tr><td></td><td>2014</td><td>2013</td></tr><tr><td>Notes with rates from 2.13% to 6.15%, due 2016 to 2042</td><td>$5,642</td><td>$5,642</td></tr><tr><td>Notes with rates from 7.00% to 7.75%, due 2016 to 2036</td><td>916</td><td>916</td></tr><tr><td>Other debt</td><td>483</td><td>476</td></tr><tr><td>Total long-term debt</td><td>7,041</td><td>7,034</td></tr><tr><td>Less: unamortized discounts</td><td>-872</td><td>-882</td></tr><tr><td>Total long-term debt, net</td><td>$6,169</td><td>$6,152</td></tr></table>
<table><tr><td></td><td colspan="5">Natural Gas and Casinghead Gas (Bcf)</td></tr><tr><td></td><td>United States</td><td>Equatorial Guinea</td><td>Israel</td><td>Other Int'l -1</td><td>Total</td></tr><tr><td>Proved Reserves as of:</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>December 31, 2007</td><td>1,840</td><td>941</td><td>319</td><td>207</td><td>3,307</td></tr><tr><td>Revisions of Previous Estimates-2</td><td>-253</td><td>34</td><td>1</td><td>8</td><td>-210</td></tr><tr><td>Extensions, Discoveries and Other Additions-3</td><td>345</td><td>78</td><td>4</td><td>-</td><td>427</td></tr><tr><td>Purchase of Minerals in Place-4</td><td>72</td><td>-</td><td>-</td><td>-</td><td>72</td></tr><tr><td>Sale of Minerals in Place-5</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Production</td><td>-145</td><td>-75</td><td>-51</td><td>-10</td><td>-281</td></tr><tr><td>December 31, 2008</td><td>1,859</td><td>978</td><td>273</td><td>205</td><td>3,315</td></tr><tr><td>Revisions of Previous Estimates-2</td><td>-397</td><td>49</td><td>-2</td><td>-</td><td>-350</td></tr><tr><td>Extensions, Discoveries and Other Additions-3</td><td>211</td><td>-</td><td>5</td><td>2</td><td>218</td></tr><tr><td>Purchase of Minerals in Place-4</td><td>6</td><td>-</td><td>-</td><td>-</td><td>6</td></tr><tr><td>Sale of Minerals in Place-5</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Production</td><td>-145</td><td>-87</td><td>-42</td><td>-11</td><td>-285</td></tr><tr><td>December 31, 2009</td><td>1,534</td><td>940</td><td>234</td><td>196</td><td>2,904</td></tr><tr><td>Revisions of Previous Estimates-2</td><td>-6</td><td>12</td><td>-41</td><td>-3</td><td>-38</td></tr><tr><td>Extensions, Discoveries and Other Additions-3</td><td>140</td><td>-</td><td>1,698</td><td>-</td><td>1,838</td></tr><tr><td>Purchase of Minerals in Place-4</td><td>139</td><td>-</td><td>-</td><td>-</td><td>139</td></tr><tr><td>Sale of Minerals in Place-5</td><td>-35</td><td>-</td><td>-</td><td>-160</td><td>-195</td></tr><tr><td>Production</td><td>-146</td><td>-83</td><td>-47</td><td>-11</td><td>-287</td></tr><tr><td>December 31, 2010</td><td>1,626</td><td>869</td><td>1,844</td><td>22</td><td>4,361</td></tr><tr><td>Proved Developed Reserves as of:</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>December 31, 2007</td><td>1,259</td><td>830</td><td>263</td><td>204</td><td>2,556</td></tr><tr><td>December 31, 2008</td><td>1,268</td><td>700</td><td>216</td><td>201</td><td>2,385</td></tr><tr><td>December 31, 2009</td><td>1,114</td><td>638</td><td>191</td><td>192</td><td>2,135</td></tr><tr><td>December 31, 2010</td><td>1,156</td><td>597</td><td>145</td><td>19</td><td>1,917</td></tr><tr><td>Proved Undeveloped Reserves as of:</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>December 31, 2007</td><td>581</td><td>111</td><td>56</td><td>3</td><td>751</td></tr><tr><td>December 31, 2008</td><td>591</td><td>278</td><td>57</td><td>4</td><td>930</td></tr><tr><td>December 31, 2009</td><td>420</td><td>302</td><td>43</td><td>4</td><td>769</td></tr><tr><td>December 31, 2010</td><td>470</td><td>272</td><td>1,699</td><td>3</td><td>2,444</td></tr></table>
<table><tr><td></td><td colspan="3">December 31,</td></tr><tr><td></td><td>2015</td><td>2014</td><td>2013</td></tr><tr><td>(millions, except percentages)</td><td></td><td></td><td></td></tr><tr><td>Cash and Cash Equivalents</td><td>$1,028</td><td>$1,183</td><td>$1,117</td></tr><tr><td>Amount Available to be Borrowed Under Credit Facility<sup>-1</sup></td><td>4,000</td><td>4,000</td><td>4,000</td></tr><tr><td>Total Liquidity</td><td>$5,028</td><td>$5,183</td><td>$5,117</td></tr><tr><td>Total Debt<sup>-2</sup></td><td>$7,976</td><td>$6,197</td><td>$4,843</td></tr><tr><td>Total Shareholders' Equity</td><td>10,370</td><td>10,325</td><td>9,184</td></tr><tr><td>Ratio of Debt-to-Book Capital<sup>-3</sup></td><td>43%</td><td>38%</td><td>35%</td></tr></table>

Question: what was the average total long-term debt from 2013 to 2014
Answer: 8.5
Reasoning program: subtract(6169,6152), divide(#0,const_2)