Investments Prior to our acquisition of Keystone on October 12, 2007, we held common shares of Keystone, which were classified as an available-for-sale investment security.
Accordingly, the investment was included in other assets at its fair value, with the unrealized gain excluded from earnings and included in accumulated other comprehensive income, net of applicable taxes.
Upon our acquisition of Keystone on October 12, 2007, the unrealized gain was removed from accumulated other comprehensive income, net of applicable taxes, and the original cost of the common shares was considered a component of the purchase price.
Fair Value of Financial Instruments Our debt is reflected on the balance sheet at cost.
Based on current market conditions, our interest rate margins are below the rate available in the market, which causes the fair value of our debt to fall below the carrying value.
The fair value of our term loans (see Note 6, “Long-Term Obligations”) is approximately $570 million at December 31, 2009, as compared to the carrying value of $596 million.
We estimated the fair value of our term loans by calculating the upfront cash payment a market participant would require to assume our obligations.
The upfront cash payment, excluding any issuance costs, is the amount that a market participant would be able to lend at December 31, 2009 to an entity with a credit rating similar to ours and achieve sufficient cash inflows to cover the scheduled cash outflows under our term loans.
The carrying amounts of our cash and equivalents, net trade receivables and accounts payable approximate fair value.
We apply the market approach to value our financial assets and liabilities, which include the cash surrender value of life insurance, deferred compensation liabilities and interest rate swaps.
The market approach utilizes available market information to estimate fair value.
Required fair value disclosures are included in Note 8, “Fair Value Measurements.
” Accrued Expenses We self-insure a portion of employee medical benefits under the terms of our employee health insurance program.
We purchase certain stop-loss insurance to limit our liability exposure.
We also self-insure a portion of our property and casualty risk, which includes automobile liability, general liability, workers’ compensation and property under deductible insurance programs.
The insurance premium costs are expensed over the contract periods.
A reserve for liabilities associated with these losses is established for claims filed and claims incurred but not yet reported based upon our estimate of ultimate cost, which is calculated using analyses of historical data.
We monitor new claims and claim development as well as trends related to the claims incurred but not reported in order to assess the adequacy of our insurance reserves.
Self-insurance reserves on the Consolidated Balance Sheets are net of claims deposits of $0.7 million and $0.8 million, at December 31, 2009 and 2008, respectively.
While we do not expect the amounts ultimately paid to differ significantly from our estimates, our insurance reserves and corresponding expenses could be affected if future claim experience differs significantly from historical trends and assumptions.
Product Warranties Some of our mechanical products are sold with a standard six-month warranty against defects.
We record the estimated warranty costs at the time of sale using historical warranty claim information to project future warranty claims activity and related expenses.
The changes in the warranty reserve are as follows (in thousands):
## Table 0 ##
requirements.
See additional information included in Critical Accounting Policies – Commodity Derivative Instruments and Item 7A.
Quantitative and Qualitative Disclosures About Market Risk.
Certain of our commodity contracts were executed in connection with the Patina Merger, prior to the global crude oil and natural gas price escalations which began in early 2005.
The settlements of these contracts have reduced our cash flows.
However, these contracts expired in December 2008.
Our remaining commodity contracts were executed in more favorable price environments.
Although we cannot predict market prices, our remaining commodity contract positions should result in more favorable cash flows as compared to our commodity contract positions in prior periods.
See Item 8.
Financial Statements and Supplementary Data – Note 6 – Derivative Instruments and Hedging Activities for our current hedge positions.
Cash Flows Summary cash flow information is as follows:
## Table 1 ##
Operating Activities—Net cash provided by operating activities totaled $2.3 billion in 2008, an increase of $268 million, or 13%, as compared with 2007.
The increase was primarily due to a significant increase in oil, gas and NGL sales resulting from higher average realized crude oil and natural gas prices during the first nine months of 2008.
The revenue increase was slightly offset by higher production costs and G&A expense.
Net cash provided by operating activities includes dividends received from equity method investees.
Net cash provided by operating activities was $2.0 billion in 2007, an increase of $287 million, or 17% as compared with 2006.
The increase was due primarily to increased sales resulting from higher average realized crude oil prices and higher average realized US natural gas prices.
These increases were partially offset by higher exploration expense and G&A expense.
In addition, cash flows from operating activities in 2007 included dividends from equity method investees.
Cash distributions from equity method investees received in 2006 were repayments of loans and were included in investing activities.
See Results of Operations—Income from Equity Method Investees.
Investing Activities—The primary use of cash in investing activities is for capital spending, which may be offset by proceeds from property sales or distributions from equity method investees.
Net cash used in investing activities totaled $2.1 billion in 2008, as compared with $1.4 billion in 2007.
In 2008 we had an expanded capital budget, with increased acquisition, development and exploratory activity in onshore US and deepwater Gulf of Mexico areas as well as increased exploratory activity in international locations including Equatorial Guinea and Israel.
Our total additions to property, plant and equipment plus acquisitions ($2.3 billion) were minimally offset by proceeds from property sales ($131 million).
In comparison, in 2007, we had additions to property, plant and equipment ($1.4 billion) primarily due to development activity in the US and North Sea and acquisition and exploratory activities in the US and West Africa.
Expenditures were minimally offset by proceeds from property sales of $9 million.
In comparison, in 2006 cash flows from investing activities totaled $1.1 billion.
We had acquisitions and additions to property, plant and equipment ($1.8 billion) due to the acquisition of U. S.  Exploration plus additional development and exploratory activity in the US and development activity in the North Sea.
These expenditures were offset by proceeds from the sale of our significant Gulf of Mexico shelf properties ($520 million) and net distributions received from equity method investees ($151 million).
The distributions from equity method investees were the result of repayment of loans and therefore were included in cash flows from investing activities.
See Results of Operations—Income from Equity Method Investees.
(4) Includes production through November 24, 2010.
Our Block 3 PSC was terminated by the Ecuadorian government on November 25, 2010.
Intercompany natural gas sales were eliminated for accounting purposes.
Electricity sales are included in other revenues.
See Termination of Ecuador PSC above.
(5) Volumes represent sales of condensate and LPG from the LPG plant in Equatorial Guinea.
Revenues from sales of crude oil and natural gas have accounted for 90% or more of consolidated revenues for each of the last three fiscal years.
At December 31, 2010, our operated properties accounted for approximately 64% of our total production.
Being the operator of a property improves our ability to directly influence production levels and the timing of projects, while also enhancing our control over operating expenses and capital expenditures.
Productive Wells The number of productive crude oil and natural gas wells in which we held an interest at December 31, 2010 was as follows:
## Table 2 ##
Productive wells are producing wells and wells mechanically capable of production.
A gross well is a well in which a working interest is owned.
The number of gross wells is the total number of wells in which a working interest is owned.
The number of net wells is the sum of the fractional working interests owned in gross wells expressed as whole numbers and fractions thereof.
Wells with multiple completions are counted as one well in the table above.
Developed and Undeveloped Acreage Developed and undeveloped acreage (including both leases and concessions) held at December 31, 2010 was as follows:
## Table 3 ##
(1) The North Sea includes acreage in the UK and the Netherlands.
(2) We are currently funding a 2-D seismic survey over the acreage in return for a working interest in the concession.
(3) A portion of the acreage has been assigned to a partner and the agreement is awaiting government approval.
Developed acreage is comprised of leased acres that are within an area spaced by or assignable to a productive well.
Undeveloped acreage is comprised of leased acres with defined remaining terms and not within an area spaced by or assignable to a productive well.
A gross acre is any leased acre in which a working interest is owned.
A net acre is comprised of the total of the owned working interest(s) in a gross acre expressed in a fractional format.
Noble Energy, Inc.  Index to Financial Statements Notes to Consolidated Financial Statements 135 crude oil and natural gas production, commodity prices based on sales contract terms or commodity price curves as of the date of the estimate, estimated operating and development costs, and a risk-adjusted discount rate of 10%.
The fair values of assets held for sale were based on anticipated sales proceeds less costs to sell.
See Note 5.
Asset Impairments.
Additional Fair Value Disclosures Debt The fair value of fixed-rate, public debt is estimated based on the published market prices for the same or similar issues.
As such, we consider the fair value of our public fixed rate debt to be a Level 1 measurement on the fair value hierarchy.
See Note 10.
Long-Term Debt.
Fair value information regarding our debt is as follows:
## Table 4 ##
(1) Net of unamortized discount, premium and debt issuance costs and excludes capital lease and other obligations.
No floating rate debt was outstanding at December 31, 2015 or December 31, 2014.
Note 14.
Earnings (Loss) Per Share Basic earnings (loss) per share of common stock is computed using the weighted average number of shares of common stock outstanding during each period.
The diluted earnings (loss) per share of common stock include the effect of outstanding stock options, shares of restricted stock, or shares of our common stock held in a rabbi trust (when dilutive).
The following table summarizes the calculation of basic and diluted earnings (loss) per share:

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Balance as of January 1, 2008	$580
Warranty expense	3,681
Warranty claims	-3,721
Balance as of December 31, 2008	540
Warranty expense	5,033
Warranty claims	-4,969
Balance as of December 31, 2009	$604

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Year Ended December 31,
2008	2007	2006
(in millions)
Total cash provided by (used in):
Operating activities	$2,285	$2,017	$1,730
Investing activities	-2,132	-1,403	-1,098
Financing activities	327	-107	-589
Increase in cash and cash equivalents	$480	$507	$43

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Crude Oil Wells	Natural Gas Wells	Total
Gross	Net	Gross	Net	Gross	Net
United States	6,543	5,759.5	6,804	4,968.1	13,347	10,727.6
Equatorial Guinea	4	1.6	13	4.4	17	6.0
Israel	-	-	6	2.8	6	2.8
North Sea	18	3.8	8	1.0	26	4.8
China	19	10.8	1	0.6	20	11.4
Total	6,584	5,775.7	6,832	4,976.9	13,416	10,752.6

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Developed Acreage	Undeveloped Acreage
Gross	Net	Gross	Net
(thousands)
United States
Onshore	1,535	1,012	1,815	1,318
Offshore	65	35	562	397
Total United States	1,600	1,047	2,377	1,715
International
Equatorial Guinea	56	19	573	233
Cameroon	-	-	1,125	563
Israel	62	29	1,592	660
North Sea-1	52	7	213	41
China	7	4	-	-
Suriname	-	-	3,087	1,389
France-2	-	-	2,808	2,036
Nicaragua	-	-	1,977	1,977
Cyprus-3	-	-	1,136	795
India	-	-	694	347
Total International	177	59	13,205	8,041
Total	1,777	1,106	15,582	9,756

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December 31,2015	December 31,2014
(millions)	Carrying Amount	Fair Value	Carrying Amount	Fair Value
Long-Term Debt, Net-1	$7,626	$7,105	$5,758	$6,179

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Question: what is the highest total amount of North Sea?
Answer: 18