EOG utilized average prices per acre from comparable market transactions and estimated discounted cash flows as the basis for determining the fair value of unproved and proved properties, respectively, received in non-cash property exchanges.
See Note 10.
Fair Value of Debt.
At December 31, 2018 and 2017, respectively, EOG had outstanding $6,040 million and $6,390 million aggregate principal amount of senior notes, which had estimated fair values of approximately $6,027 million and $6,602 million, respectively.
The estimated fair value of debt was based upon quoted market prices and, where such prices were not available, other observable (Level 2) inputs regarding interest rates available to EOG at year-end.14.
Accounting for Certain Long-Lived Assets EOG reviews its proved oil and gas properties for impairment purposes by comparing the expected undiscounted future cash flows at a depreciation, depletion and amortization group level to the unamortized capitalized cost of the asset.
The carrying values for assets determined to be impaired were adjusted to estimated fair value using the Income Approach described in the Fair Value Measurement Topic of the ASC.
In certain instances, EOG utilizes accepted offers from third-party purchasers as the basis for determining fair value.
During 2018, proved oil and gas properties with a carrying amount of $139 million were written down to their fair value of $18 million, resulting in pretax impairment charges of $121 million.
During 2017, proved oil and gas properties with a carrying amount of $370 million were written down to their fair value of $146 million, resulting in pretax impairment charges of $224 million.
Impairments in 2018, 2017 and 2016 included domestic legacy natural gas assets.
Amortization and impairments of unproved oil and gas property costs, including amortization of capitalized interest, were $173 million, $211 million and $291 million during 2018, 2017 and 2016, respectively.15.
Asset Retirement Obligations The following table presents the reconciliation of the beginning and ending aggregate carrying amounts of short-term and long-term legal obligations associated with the retirement of property, plant and equipment for the years ended December 31, 2018 and 2017 (in thousands):
## Table 0 ##
(1) Includes settlements related to asset sales.
The current and noncurrent portions of EOG's asset retirement obligations are included in Current Liabilities - Other and Other Liabilities, respectively, on the Consolidated Balance Sheets.
experience.
In each accounting period, we must make judgments and estimates of sales incentives and potential future sales returns related to current period revenue.
These estimates affect our net revenue line item on our consolidated statement of operations and affect our net accounts receivable, deferred revenue or accrued liabilities line items on our consolidated balance sheet.
Historically, there have been no significant adjustments to these estimates related to prior periods.
At December 31, 2009, our allowance for sales returns was $5.0 million compared to $2.7 million at December 28, 2008.
If our allowance for sales returns was to increase by 10%, or $0.5 million, our net revenue would decrease by $0.5 million for the year ended December 31, 2009.
Stock-Based Compensation Our stock-based compensation expense is as follows:
## Table 1 ##
Employees.
Prior to January 2, 2006, we accounted for stock-based awards to employees using the intrinsic value method in accordance with ASC 718 (formerly referred to as Accounting Principles Board (APB) Opinion No.25 and Statement of Financial Accounting Standards (SFAS No.44).
Effective January 2, 2006, we adopted ASC 718 (SFAS 123R).
For stock option grants made subsequent to January 2, 2006, we have accounted for such stock-based awards to employees in accordance with ASC 718 (SFAS 123R), which requires compensation expense related to share-based transactions, including employee stock options, to be measured and recognized in the financial statements based on a determination of the fair value of the stock options.
The grant date fair value is determined using the Black-Scholes-Merton (“Black-Scholes”) pricing model.
We adopted ASC 718 (SFAS 123R) using the prospective method, in which non-public entities that previously applied ASC 718 (SFAS 123R) using the minimum value method, whether for financial statement recognition or pro forma disclosure purposes, would continue to account for unvested stock options outstanding at the date of adoption of ASC 718 (SFAS 123R) in the same manner as they had been accounted for prior to the adoption of ASC 718 (SFAS 123R).
We will continue to apply ASC 718 (APB 25) in future periods to stock options issued and outstanding at January 2, 2006.
For all employee stock options, we recognize expense over the requisite service period using the straightline method.
There is a risk that our estimates of the fair values of our stock-based compensation awards on the grant dates may bear little resemblance to the actual values realized upon exercise.
Stock options may expire or otherwise result in zero intrinsic value as compared to the fair values originally estimated on the grant date and reported in our financial statements.
Alternatively, value may be realized from these instruments that are significantly higher than the fair values originally estimated on the grant date and reported in our financial statements.
As of the end of fiscal years 2009, 2008 and 2007, there was approximately $17.5 million, $13.6 million and $4.1 million, respectively, of unrecognized stock-based compensation expense related to non-vested stock option awards, net of estimated forfeitures, that we expect to be recognized over a weighted-average period of 2.61, 2.77 and 1.47 years, respectively.
## Table 2 ##
Fiscal Years 2010 and 2009 Revenue
## Table 3 ##
Total revenue increased $72.6 million, or 28.8%, in fiscal 2010 compared to fiscal 2009.
The Americas region contributed the largest portion of this growth.
Product revenue increased $36.5 million, or 36.9%, compared to fiscal 2009.
The increase in product revenue was primarily driven by higher product sales volume across all regions.
When looking at the mix of product revenue, there was a greater mix of our high-end products due to increased sales to enterprise and service provider customers as evidenced by a 79% increase in the number of $500,000+ deals in fiscal 2010 compared to fiscal 2009.
Services revenue increased $32.9 million, or 23.6%, in fiscal 2010 compared to fiscal 2009 due to the recognition of revenue from our growing deferred revenue balance consisting of subscription and support contracts sold to a larger customer base and our increased focus on contract renewals.
The growth in services revenue tends to lag growth in billings and product revenue due to amortization of revenue over the service period.
The growth in ratable product and services revenue was due to a slight decrease in the weighted-average service period as a result of a decrease in the average contractual term of support contracts for arrangements in which we recognized product and services revenue ratably.
Financing Activities In fiscal 2010, our financing activities resulted in net cash provided of $34.0 million as a result of receiving proceeds of $29.1 million from the exercise of stock options and warrants to purchase our common stock and an excess tax benefit from employee stock option plans of $5.8 million related to option exercises, partially offset by $0.9 million of issuance costs paid in connection with our initial public offering, which had been accrued as of December 31, 2009.
In fiscal 2009, our financing activities resulted in net cash provided of $78.0 million as a result of receiving proceeds of $91.5 million, net of issuance costs paid of $3.3 million, from the sale of common stock in connection with our initial public offering in November 2009.
In addition, we received proceeds of $4.0 million from the exercise of stock options and warrants to purchase our common stock and had an in excess tax benefit from employee stock option plans of $1.6 million, all partially offset by $15.8 million related to the repurchase of our preferred and common stock in the first half of fiscal 2009.
In fiscal 2008, our financing activities related to proceeds of $2.1 million, as a result of exercises of stock options to purchase our common stock.
Contractual Obligations and Commitments The following summarizes our contractual obligations as of December 31, 2010:

<table><tr><td></td><td>2018</td><td>2017</td></tr><tr><td>Carrying Amount at Beginning of Period</td><td>$946,848</td><td>$912,926</td></tr><tr><td>Liabilities Incurred</td><td>79,057</td><td>54,764</td></tr><tr><td>Liabilities Settled<sup>-1</sup></td><td>-70,829</td><td>-61,871</td></tr><tr><td>Accretion</td><td>36,622</td><td>34,708</td></tr><tr><td>Revisions</td><td>-38,932</td><td>-9,818</td></tr><tr><td>Foreign Currency Translations</td><td>1,611</td><td>16,139</td></tr><tr><td>Carrying Amount at End of Period</td><td>$954,377</td><td>$946,848</td></tr><tr><td>Current Portion</td><td>$26,214</td><td>$19,259</td></tr><tr><td>Noncurrent Portion</td><td>$928,163</td><td>$927,589</td></tr></table>
<table><tr><td rowspan="3"></td><td colspan="3"> Fiscal Year</td></tr><tr><td> 2009</td><td> 2008</td><td> 2007</td></tr><tr><td colspan="3"> (in thousands)</td></tr><tr><td>Cost of product revenue</td><td>$102</td><td>$67</td><td>$553</td></tr><tr><td>Cost of services revenue</td><td>658</td><td>400</td><td>416</td></tr><tr><td>Research and development</td><td>1,963</td><td>1,049</td><td>1,452</td></tr><tr><td>Sales and marketing</td><td>3,020</td><td>2,512</td><td>3,928</td></tr><tr><td>General and administrative</td><td>1,718</td><td>1,271</td><td>2,983</td></tr><tr><td>Total stock-based compensation</td><td>$7,461</td><td>$5,299</td><td>$9,332</td></tr></table>
<table><tr><td rowspan="3"></td><td colspan="3">Fiscal Year</td></tr><tr><td>2010</td><td>2009</td><td>2008</td></tr><tr><td colspan="3">(as % of revenue)</td></tr><tr><td>Revenue</td><td></td><td></td><td></td></tr><tr><td>Product</td><td>41.6</td><td>39.1</td><td>44.7</td></tr><tr><td>Services</td><td>53.0</td><td>55.2</td><td>49.7</td></tr><tr><td>Ratable product and services</td><td>5.4</td><td>5.7</td><td>5.6</td></tr><tr><td>Total revenue</td><td>100.0</td><td>100.0</td><td>100.0</td></tr><tr><td>Total cost of revenue</td><td>26.2</td><td>27.8</td><td>30.9</td></tr><tr><td>Total gross profit</td><td>73.8</td><td>72.2</td><td>69.1</td></tr><tr><td>Operating expenses</td><td></td><td></td><td></td></tr><tr><td>Research and development</td><td>15.3</td><td>16.7</td><td>17.5</td></tr><tr><td>Sales and marketing</td><td>34.6</td><td>38.2</td><td>41.4</td></tr><tr><td>General and administrative</td><td>6.9</td><td>7.3</td><td>7.9</td></tr><tr><td>Total operating expenses</td><td>56.8</td><td>62.2</td><td>66.8</td></tr><tr><td>Operating income</td><td>17.0</td><td>10.0</td><td>2.3</td></tr><tr><td>Interest income</td><td>0.7</td><td>0.8</td><td>1.3</td></tr><tr><td>Other income (expense), net</td><td>-0.2</td><td>0.1</td><td>0.8</td></tr><tr><td>Income before provision for income taxes</td><td>17.5</td><td>10.9</td><td>4.4</td></tr><tr><td>Provision for (benefit from) income taxes</td><td>4.6</td><td>-13.0</td><td>0.9</td></tr><tr><td>Net income</td><td>12.9</td><td>23.9</td><td>3.5</td></tr></table>
<table><tr><td rowspan="4"></td><td colspan="4">Fiscal Year</td><td></td><td></td></tr><tr><td colspan="2">2010</td><td colspan="2">2009</td><td></td><td></td></tr><tr><td>Amount ($)</td><td>% ofRevenue</td><td>Amount ($)</td><td>% ofRevenue</td><td>$ Change</td><td>% Change</td></tr><tr><td colspan="6">($ amounts in 000's)</td></tr><tr><td>Revenue:</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Product</td><td>135,140</td><td>41.6</td><td>98,686</td><td>39.1</td><td>36,454</td><td>36.9</td></tr><tr><td>Services</td><td>172,046</td><td>53.0</td><td>139,172</td><td>55.2</td><td>32,874</td><td>23.6</td></tr><tr><td>Ratable product and services</td><td>17,510</td><td>5.4</td><td>14,257</td><td>5.7</td><td>3,253</td><td>22.8</td></tr><tr><td>Total revenue</td><td>324,696</td><td>100.0</td><td>252,115</td><td>100.0</td><td>72,581</td><td>28.8</td></tr><tr><td>Revenue by Geography:</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Americas</td><td>123,961</td><td>38.2</td><td>92,621</td><td>36.7</td><td>31,340</td><td>33.8</td></tr><tr><td>EMEA</td><td>121,604</td><td>37.5</td><td>95,886</td><td>38.1</td><td>25,718</td><td>26.8</td></tr><tr><td>APAC</td><td>79,131</td><td>24.3</td><td>63,608</td><td>25.2</td><td>15,523</td><td>24.4</td></tr><tr><td>Total revenue</td><td>324,696</td><td>100.0</td><td>252,115</td><td>100.0</td><td>72,581</td><td>28.8</td></tr></table>

Question: When does Ratable product and services reach the largest value?
Answer: 2010