BUSINESS ENVIRONMENT The following discussion and analysis summarizes the significant factors affecting our results of operations, financial condition and liquidity position as of and for the year ended December 31, 2018, 2017 and 2016, and should be read in conjunction with the consolidated and combined financial statements and related notes of the Company.
We operate in more than 120 countries helping customers find, evaluate, drill, produce, transport and process hydrocarbon resources.
Our revenue is predominately generated from the sale of products and services to major, national, and independent oil and natural gas companies worldwide, and is dependent on spending by our customers for oil and natural gas exploration, field development and production.
This spending is driven by a number of factors, including our customers' forecasts of future energy demand and supply, their access to resources to develop and produce oil and natural gas, their ability to fund their capital programs, the impact of new government regulations and most importantly, their expectations for oil and natural gas prices as a key driver of their cash flows.
Oil and Natural Gas Prices Oil and natural gas prices are summarized in the table below as averages of the daily closing prices during each of the periods indicated.
## Table 0 ##
(1) Energy Information Administration (EIA) Europe Brent Spot Price per Barrel (2) EIA Cushing, OK WTI (West Texas Intermediate) spot price (3) EIA Henry Hub Natural Gas Spot Price per million British Thermal Unit 2018 demonstrated the volatility of the oil and gas market.
Through the first three quarters of 2018, we experienced stability in the North American and international markets.
However, in the fourth quarter of 2018 commodity prices dropped nearly 40% resulting in increased customer uncertainty.
From an offshore standpoint, through most of 2018, we saw multiple large offshore projects reach positive final investment decisions, and the LNG market and outlook improved throughout 2018, driven by increased demand globally.
In 2018, the first large North American LNG positive final investment decision was reached.
Outside of North America, customer spending is highly driven by Brent oil prices, which increased on average throughout the year.
Average Brent oil prices increased to $71.34/Bbl in 2018 from $54.12/Bbl in 2017, and ranged from a low of $50.57/Bbl in December 2018, to a high of $86.07/Bbl in October 2018.
For the first three quarters of 2018, Brent oil prices increased sequentially.
However, in the fourth quarter, Brent oil prices declined 39% versus the end of the third quarter, as a result of increased supply from the U. S. , worries of a global economic slowdown, and lower than expected production cuts.
In North America, customer spending is highly driven by WTI oil prices, which similar to Brent oil prices, on average increased throughout the year.
Average WTI oil prices increased to $65.23/Bbl in 2018 from $50.80/Bbl in 2017, and ranged from a low of $44.48/Bbl in December 2018, to a high of $77.41/Bbl in June 2018.
In North America, natural gas prices, as measured by the Henry Hub Natural Gas Spot Price, averaged $3.15/ mmBtu in 2018, representing a 6% increase over the prior year.
Throughout the year, Henry Hub Natural Gas Spot Prices ranged from a high of $6.24/mmBtu in January 2018 to a low of $2.49/mmBtu in February 2018.
According to the U. S.  Department of Energy (DOE), working natural gas in storage at the end of 2018 was 2,705 billion cubic feet (Bcf), which was 15.6%, or 421 Bcf, below the corresponding week in 2017.
ESSEX PORTFOLIO, L. P.  AND SUBSIDIARIES NOTES TO CONSOLIDATED FINANCIAL STATEMENTS December 31, 2015, 2014, and 2013 (7) Unsecured Debt ESS does not have any indebtedness as all debt is incurred by the Operating Partnership.
ESS guarantees the Operating Partnership’s unsecured debt including the revolving credit facilities up to the maximum amounts and for the full term of the facilities.
Unsecured debt consists of the following as of December 31, 2015 and 2014 ($ in thousands)
## Table 1 ##
(1) Includes unamortized premium and discounts of $14.3 million and $27.5 million and reduced by unamortized debt issuance costs of $15.6 million and $13.9 million as of December 31, 2015 and 2014, respectively.
(2) Includes unamortized debt issuance costs of $3.3 million and $3.6 million as of December 31, 2015 and 2014, respectively.
As of December 31, 2015 and 2014, the Company had $465.0 million of private placement unsecured bonds outstanding at an average effective interest rate of 4.5%.
The following is a summary of the Company’s unsecured private placement bonds as of December 31, 2015 and 2014 ($ in thousands):
## Table 2 ##
As of December 31, 2015 and 2014, the Company had unsecured term loans outstanding of $225.0 million at an average interest rate of 2.4%.
These loans are included in the line ‘‘Term loan-variable rate’’ in the table above, and as of December 31, 2015 and 2014, the carrying value net of debt issuance costs was $224.5 million and $224.1 million, respectively.
The term loans are at a variable interest rate of LIBOR plus 1.05%.
The Company entered into interest rate swap contracts for a term of five years with a notional amount totaling $225.0 million, which effectively converted the interest rate on $225.0 million of the term loans to a fixed rate of 2.4%.
The $200 million tranche of this unsecured term loan has a maturity date of November 2016 and the $25 million tranche has a maturity date of August 2017.
In March 2015, the Company issued $500.0 million of senior unsecured notes due on April 1, 2025 with a coupon rate of 3.5% per annum and are payable on April 1st and October 1st of each year, beginning October 1, 2015 (the 2025 Notes).
The 2025 Notes were offered to investors at a price of 99.747% of par value.
The 2025
The Company expects to fund the development and predevelopment pipeline by using a combination of some or all of the following sources: its working capital, amounts available on its lines of credit, construction loans, net proceeds from public and private equity and debt issuances, and proceeds from the disposition of properties, if any.
Redevelopment Pipeline The Company defines redevelopment communities as existing properties owned or recently acquired, which have been targeted for additional investment by the Company with the expectation of increased financial returns through property improvement.
During redevelopment, apartment homes may not be available for rent and, as a result, may have less than stabilized operations.
As of December 31, 2015, the Company had ownership interests in five major redevelopment communities aggregating 1,313 apartment homes with estimated redevelopment costs of $159.8 million, of which approximately $82.5 million remains to be expended.
Alternative Capital Sources The Company utilizes co-investments as an alternative source of capital for acquisitions of both operating and development communities.
As of December 31, 2015, the Company had an interest in 1,676 apartment homes of communities actively under development with joint ventures for a total estimated cost of $0.9 billion.
Total estimated remaining costs total approximately $500.0 million, of which the Company estimates that its remaining investment in these development joint ventures will be approximately $255.0 million.
In addition, the Company had an interest in 10,520 apartment homes of operating communities with joint ventures for a total book value of $738.9 million.
Contractual Obligations and Commercial Commitments The following table summarizes the maturity or due dates of the Company’s contractual obligations and other commitments at December 31, 2015, and the effect such obligations could have on the Company’s liquidity and cash flow in future periods ($ in thousands):
## Table 3 ##
(1) Interest on indebtedness for variable debt was calculated using interest rates as of December 31, 2015.
(2) Estimated project cost for development the Company’s 500 Folsom project is net of a projected value for low-income housing tax credit proceeds and savings from tax exempt bonds.
Variable Interest Entities In accordance with accounting standards for consolidation of variable interest entities (VIEs), the Company consolidates the Operating Partnership and 19 DownREIT limited partnerships (comprising eleven communities).
The Company consolidates these entities because it is deemed the primary beneficiary.
The REIT has no assets or liabilities other than its investment in the Operating Partnership.
The consolidated total assets and liabilities related to these DownREIT VIEs, net of intercompany eliminations, were approximately $241.0 million and $206.7 million, respectively, as of December 31, 2015, and $235.1 million and $209.1 million respectively, as of December 31, 2014.
Interest holders in VIEs consolidated by the Company are allocated net income equal to the cash payments made to those interest holders for services rendered or distributions from cash flow.
The remaining results of operations are generally allocated to the Company.
As of December 31, 2015, the Company did not have any VIE’s of which it was not deemed to be the primary beneficiary
ESSEX PORTFOLIO, L. P.  AND SUBSIDIARIES NOTES TO CONSOLIDATED FINANCIAL STATEMENTS December 31, 2015, 2014, and 2013 A summary of the fair value of the assets and liabilities acquired on April 1, 2014 was as follows (includes the 14 properties acquired on March 31, 2014 as the OP Units issued were retired on April 1, 2014) (in millions):
## Table 4 ##
During the quarter ended March 31, 2015 the Company recorded adjustments to decrease the preliminary fair value of real property by $13.1 million, to increase the preliminary fair value of co-investments by $6.0 million and to decrease its preliminary estimate for liabilities assumed by $7.1 million.
The change in estimates were the result of subsequent additional information pertaining to the opening balance sheet identified by management.
The Company believes that the information gathered to date provides a reasonable basis for estimating the fair values of assets acquired and liabilities assumed.
Due to these adjustments and, certain amounts do not agree to previously reported balances.
(3) Real Estate Investments (a) Acquisitions of Real Estate For the year ended December 31, 2015, the Company purchased seven communities consisting of 1,722 apartment homes for $638.1 million.
The table below summarizes acquisition activity for the year ended December 31, 2015 ($ in millions):
## Table 5 ##
(1) In March 2015, the Company purchased the joint venture partner’s remaining membership interest in The Huxley and The Dylan co-investments for a purchase price of $100.1 million.
The properties are now consolidated.
(2) In April 2015, the Company purchased the joint venture partner’s 49.5% membership interest in the Reveal co-investment for a purchase price of $73.0 million.
The property is now consolidated.
The $638.1 million aggregate purchase price for the acquisitions listed above were included on the Company’s consolidated balance sheet as follows: $117.9 million was included in land and land improvements,

<table><tr><td></td><td>2018</td><td>2017</td><td>2016</td></tr><tr><td>Brent oil prices ($/Bbl)<sup>(1)</sup></td><td>$71.34</td><td>$54.12</td><td>$43.64</td></tr><tr><td>WTI oil prices ($/Bbl)<sup>(2)</sup></td><td>65.23</td><td>50.80</td><td>43.29</td></tr><tr><td>Natural gas prices ($/mmBtu)<sup>(3)</sup></td><td>3.15</td><td>2.99</td><td>2.52</td></tr></table>
<table><tr><td></td><td>2015</td><td>2014</td><td>Weighted AverageMaturityIn Years</td></tr><tr><td>Unsecured bonds private placement - fixed rate</td><td>$463,891</td><td>$463,443</td><td>3.2</td></tr><tr><td>Term loan - variable rate</td><td>224,467</td><td>224,130</td><td>0.9</td></tr><tr><td>Bonds public offering - fixed rate</td><td>2,400,322</td><td>1,915,975</td><td>6.7</td></tr><tr><td>Unsecured debt, net<sup>-1</sup></td><td>3,088,680</td><td>2,603,548</td><td></td></tr><tr><td>Lines of credit, net<sup>-2</sup></td><td>11,707</td><td>242,824</td><td></td></tr><tr><td>Total unsecured debt</td><td>$3,100,387</td><td>$2,846,372</td><td></td></tr><tr><td>Weighted average interest rate on fixed rate unsecured and unsecured private placement bonds</td><td>3.6%</td><td>3.6%</td><td></td></tr><tr><td>Weighted average interest rate on variable rate term loan</td><td>2.4%</td><td>2.4%</td><td></td></tr><tr><td>Weighted average interest rate on lines of credit</td><td>1.9%</td><td>1.8%</td><td></td></tr></table>
<table><tr><td></td><td>Maturity</td><td>2015</td><td>2014</td><td>CouponRate</td></tr><tr><td>Senior unsecured private placement notes</td><td>March 2016</td><td>$150,000</td><td>$150,000</td><td>4.36%</td></tr><tr><td>Senior unsecured private placement notes</td><td>September 2017</td><td>40,000</td><td>40,000</td><td>4.50%</td></tr><tr><td>Senior unsecured private placement notes</td><td>December 2019</td><td>75,000</td><td>75,000</td><td>4.92%</td></tr><tr><td>Senior unsecured private placement notes</td><td>April 2021</td><td>100,000</td><td>100,000</td><td>4.27%</td></tr><tr><td>Senior unsecured private placement notes</td><td>June 2021</td><td>50,000</td><td>50,000</td><td>4.30%</td></tr><tr><td>Senior unsecured private placement notes</td><td>August 2021</td><td>50,000</td><td>50,000</td><td>4.37%</td></tr><tr><td></td><td></td><td>$465,000</td><td>$465,000</td><td></td></tr></table>
<table><tr><td></td><td>2016</td><td>2017 and2018</td><td>2019 and2020</td><td>Thereafter</td><td>Total</td></tr><tr><td>Mortgage notes payable</td><td>$29,714</td><td>$519,802</td><td>$1,279,300</td><td>$329,451</td><td>$2,158,267</td></tr><tr><td>Unsecured debt</td><td>350,000</td><td>365,000</td><td>75,000</td><td>2,300,000</td><td>3,090,000</td></tr><tr><td>Lines of credit</td><td>—</td><td>—</td><td>15,000</td><td>—</td><td>15,000</td></tr><tr><td>Interest on indebtedness<sup>-1</sup></td><td>221,917</td><td>373,819</td><td>266,313</td><td>223,734</td><td>1,085,783</td></tr><tr><td>Ground leases</td><td>2,742</td><td>5,484</td><td>5,484</td><td>131,851</td><td>145,561</td></tr><tr><td>Operating leases</td><td>1,695</td><td>3,557</td><td>3,792</td><td>12,350</td><td>21,394</td></tr><tr><td>Development commitments (including co-investments)<sup>(2)</sup></td><td>195,218</td><td>329,207</td><td>17,235</td><td>—</td><td>541,660</td></tr><tr><td></td><td>$801,286</td><td>$1,596,869</td><td>$1,662,124</td><td>$2,997,386</td><td>$7,057,665</td></tr></table>
<table><tr><td>Cash assumed</td><td>$140</td></tr><tr><td>Rental properties and real estate under development</td><td>5,605</td></tr><tr><td>Real estate held for sale, net</td><td>108</td></tr><tr><td>Co-investments</td><td>224</td></tr><tr><td>Acquired in-place lease value</td><td>77</td></tr><tr><td>Other assets</td><td>16</td></tr><tr><td>Mortgage notes payable and unsecured debt</td><td>-1,747</td></tr><tr><td>Other liabilities</td><td>-87</td></tr><tr><td>Redeemable noncontrolling interest</td><td>-5</td></tr><tr><td></td><td>$4,331</td></tr><tr><td>Cash consideration for BRE merger</td><td>$556</td></tr><tr><td>Equity consideration for BRE merger</td><td>3,775</td></tr><tr><td>Total consideration for BRE merger</td><td>$4,331</td></tr></table>
<table><tr><td>Property Name</td><td>Location</td><td>Apartment Homes</td><td>Essex Ownership Percentage</td><td>Quarter in 2015</td><td>Purchase Price</td></tr><tr><td>8th & Hope</td><td>Los Angeles, CA</td><td>290</td><td>100%</td><td>Q1</td><td>$200.0</td></tr><tr><td>The Huxley<sup>-1</sup></td><td>Los Angeles, CA</td><td>187</td><td>100%</td><td>Q1</td><td>48.8</td></tr><tr><td>The Dylan<sup>-1</sup></td><td>Los Angeles, CA</td><td>184</td><td>100%</td><td>Q1</td><td>51.3</td></tr><tr><td>Reveal<sup>-2</sup></td><td>Woodland Hills, CA</td><td>438</td><td>99.75%</td><td>Q2</td><td>73.0</td></tr><tr><td>Avant</td><td>Los Angeles, CA</td><td>247</td><td>100%</td><td>Q2</td><td>99.0</td></tr><tr><td>Avant II</td><td>Los Angeles, CA</td><td>193</td><td>100%</td><td>Q4</td><td>73.0</td></tr><tr><td>Enso</td><td>San Jose, CA</td><td>183</td><td>100%</td><td>Q4</td><td>93.0</td></tr><tr><td colspan="2">Total 2015</td><td>1,722</td><td></td><td></td><td>$638.1</td></tr></table>

Question: What's the average of Unsecured debt, net of 2015, and Lines of credit of 2019 and2020 ?
Answer: 1551840.0