Exhibit 99.1

NW Natural Reports Results for the

Quarter & Six Months Ended June 30, 2011

PORTLAND, ORE.—Northwest Natural Gas Company, dba NW Natural (NYSE: NWN), reported net income for the second quarter of 2011 of $2.2 million or 8 cents per share. These results include an after-tax charge of $4.4 million (17 cents per share) related to the repeal of utility tax legislation in Oregon. Last year, the company reported net income of $6.9 million or 26 cents per share, including after tax income of $0.6 million or 2 cents per share related to repealed utility tax legislation.

For the six-months ended June 30, 2011, net income was $43.0 million or $1.61 per share, which compares to $50.5 million or $1.90 per share for the same period in 2010. Both periods include the effects of repealed utility tax legislation in Oregon. Included in the six month period of 2011 was a charge of $4.4 million after-tax or 17 cents per share, compared to income of $2.3 million after-tax or 9 cents per share in 2010, from the utility tax legislation. Results for 2010 also include the previously disclosed net refund of property taxes received in the first quarter of 2010 of $6.1 million or 14 cents per share.

Oregon utilities tax legislation enacted in quarter

On May 24, 2011, Governor Kitzhaber of Oregon signed Senate Bill 967 (SB 967) into law to repeal existing statutes from Senate Bill 408 (SB 408), which became law in 2005. SB 408 imposed on certain utilities in Oregon an annual regulatory adjustment for income taxes paid. SB 967 repealed the adjustment for income taxes retroactive to the beginning of 2010. As a result, NW Natural recorded a one-time charge of $7.4 million in the second quarter of 2011 ($4.4 million after tax or 17 cents per share) related to the repeal of SB 408 for 2010. For the three- and six-month results ended June 30, 2011, the company did not record any amount related to the SB 408 rule because of the uncertainty surrounding its repeal and the ability to collect amounts in future years based on the legislative events mentioned above.

NW Natural’s income taxes paid resulted in additional revenues to the company for every year SB 408 was in effect. For the 2008 and 2009 tax years, the Public Utility Commission of Oregon (OPUC) approved the company’s recovering $0.2 million and $5.1 million, respectively, from utility customers. The 2008 amount, plus accrued interest was collected over a one-year period beginning June 1, 2010. The 2009 surcharge, plus accrued interest, was approved for collection over a one-year period beginning June 1, 2011. As indicated earlier, the new law requires utilities including NW Natural to reverse regulatory adjustments recognized under SB 408 related to the 2010 and 2011 tax years. SB 967 now requires the OPUC to make decisions in future ratemaking proceedings on the amount of income taxes to be recovered in rates.

Customer growth rate remains around 1 percent

NW Natural’s customer growth rate for the trailing 12-month period ending June 30, 2011 was 0.8 percent, with the company adding approximately 5,600 new customers in the period. This compared to an annual growth rate of 1.0 percent a year ago.

Operating results for the quarter

The company’s utility operations, which include the effect of utility tax legislation, earned $1.1 million (4 cents per share), compared to $4.6 million (17 cents per share) in the same quarter of 2010. Gas storage contributed net income of $1.3 million (5 cents per share) in the 2011 quarter, compared to net income of $2.1 million (8 cents per share) in 2010’s second quarter. Other non-utility activities reported a slight loss of 1 cent per share in 2011’s second quarter, compared to a gain of 1 cent per share in 2010’s second quarter.

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NW Natural’s total gas sales and transportation deliveries in the second quarter of 2011, excluding deliveries of gas stored for others, were 243 million therms, up 4 percent from 233 million therms in 2010’s second quarter. The increase in usage was mainly due to weather that was 10 percent colder than a year ago and 38 percent colder than average. Margin from utility operations in 2011 decreased 10 percent to $60.0 million, compared to $66.9 million in 2010, due to repeal of the utility tax legislation mentioned above, offset in part by colder weather and customer growth.

Volumes sold to residential and commercial customers in the second quarter of 2011 were 130 million therms, up 8 percent from 120 million therms in the second quarter of 2010 due mainly to colder weather. Utility margins from residential and commercial customers in the quarter totaled $58 million, including weather normalization and decoupling adjustments, which were up 3 percent over second-quarter 2010 margin of $57 million. NW Natural’s weather and decoupling mechanisms in Oregon adjusted margin down by $2.6 million in 2011, compared to a margin adjustment decrease of $0.8 million in the second quarter of 2010, primarily driven by weather that was colder than average in the period.

Gas deliveries to industrial customers in the second quarter of 2011 were down 1 percent from 113 million therms in 2010’s second quarter. Margin from industrial customers decreased 4 percent to $6.8 million from $7.1 million in 2010’s second quarter.

Gas storage business update

The company’s gas storage business segment primarily consists of non-utility investments at the company’s Mist underground storage facility in Oregon, investments at the Gill Ranch Storage (GRS) underground facility in California, and asset optimization services using available gas storage and transportation capacity.

NW Natural’s gas storage segment reported net income of $1.3 million on net operating revenues of $7.2 million in the second quarter of 2011, compared to $2.1 million and $5.2 million, respectively, in last year’s second quarter. These results primarily reflect first year costs at GRS including depreciation, and low storage prices in California, and a decrease in optimization revenues at the company’s Mist storage operations in Oregon.

Gas reserves update

As previously reported, NW Natural received approval in the second quarter of 2011 from the OPUC to participate in a joint venture with Encana Oil & Gas (USA) Inc. to develop gas reserves on behalf of NW Natural’s utility customers. The company is expected to invest approximately $45-55 million a year over a five-year period, for a total investment of about $250 million. The investment will cover a portion of the expected drilling costs in exchange for working interests in two sections of the Jonah Field, which is located north of Rock Springs, Wyo. The drilling area includes both future and currently producing wells. By the end of the second quarter, gas production had already started from the field.

O&M costs reflect Gill Ranch start-up

Operations and maintenance expense was 7 percent higher in the second quarter of 2011, compared to 2010, primarily due to operating costs at Gill Ranch Storage, which became operational in late 2010. Utility O&M expense increased 1 percent in the quarter.

Year-to-date (six month) financial and operating highlights

The company’s utility operations, which includes the effect of utility tax legislation discussed above, contributed net income of $41.2 million ($1.54 per share), compared to $45.5 million ($1.71 per share), in the first six months of 2010. Gas storage contributed $2.0 million (8 cents per share), which compares to $4.6 million (18 cents per share) in the same period of last year. Other non-utility activities contributed a net loss of $0.3 million, compared to net income of $0.3 million last year.

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Operating results

NW Natural’s total gas sales and transportation deliveries in the first six months of 2011, excluding deliveries of gas stored for others, were 644 million therms, up 14 percent from 567 million therms in 2010. The increase in usage was mainly due to weather that was 17 percent colder than a year ago and 14 percent colder than average. Margin from utility operations in 2011 decreased 2 percent to $189.2 million, compared to $192.4 million in 2010, due to the repeal of utility tax legislation discussed above, offset in part by colder weather and customer growth.

Volumes sold to residential and commercial customers in the first six months of 2011 were 405 million therms, up 22 percent from 333 million therms in the first six months of 2010 due mainly to colder weather. Utility margin from residential and commercial customers in the first six months totaled $178 million, including weather normalization and decoupling adjustments, up 5 percent over margin in the first six months of 2010 of $170 million. NW Natural’s weather and decoupling mechanisms adjusted margin up by $0.3 million in 2011, compared to a margin adjustment increase of $20.6 million in the six months ended 2010. The results for 2010 were largely driven by weather that was significantly warmer than average in the period.

Gas deliveries to industrial customers in the first six months of 2011 were 239 million therms, or 2 percent higher than 234 million therms in the same period last year. Margin from industrial customers increased 1 percent to $14.5 million.

The company’s gas cost incentive sharing mechanism in Oregon provided a margin contribution of $1.1 million in the first six months of 2011 compared to a contribution of $0.7 million in the first six months of 2010.

Under the company’s annual purchased gas adjustment mechanism, results are subject to an earnings review to determine if the utility is earning above its authorized return on equity. Based upon current projections, the company accrued an estimated provision of $0.4 million during the six months ended June 30, 2011.

Operations and maintenance costs

Operations and maintenance expense was 4 percent higher in the first six months of 2011, compared to 2010, primarily due to operating costs at Gill Ranch Storage, which became operational in the fourth quarter of 2010. The company’s utility operations and maintenance expenses were down 1 percent from the previous year. Utility bad debt expense as a percent of revenues was well below 1 percent at 0.24 percent for the 12 months ended June 30, 2011.

Other taxes

In January 2010, the Oregon Supreme Court ruled in the company’s favor regarding litigation with the Oregon Department of Revenue over whether certain inventories held for resale should be taxed as personal property. As a result of the Oregon Supreme Court ruling, the company was refunded a net $6.1 million in the first quarter of 2010 related to taxes paid in earlier years.

Cash flows and capital structure

Cash provided by operations in the first six months of 2011 was $169 million, compared to $104 million in 2010. The increase was primarily due to working capital timing differences, partially offset by lower net income.

NW Natural’s capitalization at June 30, 2011 reflected 47.9 percent common equity, 37.0 percent long-term debt, and 15.1 percent short-term debt and current maturities of long-term debt. This compared to 48.2 percent common equity, 41.2 percent long-term debt, and 10.6 percent of short-term debt and current maturities of long-term debt at June 30, 2010.

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Outlook for 2011

Due to the repeal of utility tax legislation discussed above, earnings are expected to fall below the company’s previously stated 2011 earnings guidance of $2.45 to $2.65 per share, to a new revised guidance range of $2.28 to 2.48 per share. The company’s 2011 earnings guidance assumes continued slow economic recovery and customer growth, normal weather conditions, ongoing benefits from improvements to our cost structure, Gill Ranch operational losses due to first year operations, and no further significant changes in prevailing legislative and regulatory policies. The company’s outlook does not include forecasts of future gains or losses that may occur from the company’s gas cost sharing mechanism in Oregon since the company cannot predict future gas cost increases or decreases with reasonable certainty.

Dividend declaration

The board of directors of NW Natural declared a quarterly dividend of 43.5 cents a share on the company’s common stock on July 1, 2011. The dividends will be payable on Aug. 15, 2011 to shareholders of record on July 29, 2011. The company’s indicated annual dividend rate is $1.74 per share.

Presentation of results

In addition to presenting results of operations and earnings amounts in total, NW Natural has expressed certain measures in this press release on an equivalent cents per share basis. These amounts reflect factors that directly impact the company’s earnings. In calculating these financial measures, we allocate income tax expense based on the effective tax rate. NW Natural believes this per share information is useful because it enables readers to better understand the impact of these factors on its earnings.

Conference call arrangements

As previously reported, NW Natural will conduct a conference call and webcast starting at 8 a.m. Pacific Time (11 a.m. Eastern Time) on August 3rd, to review the company’s 2011 second quarter and year-to-date financial and operating results. To hear the conference call live, please dial 1-877-317-6789 within the United States and 1-866-605-3852 from Canada. International callers can dial 1-412-317-6789. To access the conference replay, please call 1-877-344-7529 and enter the conference identification pass code (10001724). To hear the replay from international locations, please dial 1-412-317-0088.

To hear the conference by webcast, log on to NW Natural’s corporate website at www.nwnatural.com.

Forward-looking statements

This report, and other presentations made by NW Natural from time to time, may contain forward-looking statements within the meaning of the U.S. Private Securities Litigation Reform Act of 1995. Forward-looking statements can be identified by words such as “anticipates,” “intends,” “plans,” “seeks,” “believes,” “estimates,” “expects” and similar references to future periods. Examples of forward-looking statements include, but are not limited to, statements regarding the following: plans, objectives, goals, strategies, future events, investments, projected accruals, estimated gas reserves and their financial value, customer growth, weather, customer refunds, continued drilling, project costs, commodity costs, financial positions, revenues and earnings, dividends, performance, legislative actions and impact, regulatory actions or approvals, and other statements that are other than statements of historical facts.

Forward-looking statements are based on our current expectations and assumptions regarding our business, the economy and other future conditions. Because forward-looking statements relate to the future, they are subject to inherent uncertainties, risks and changes in circumstances that are difficult to predict. Our actual results may differ materially from those contemplated by the forward-looking statements. We caution you therefore against relying on any of these forward-looking statements. They are neither statements of historical fact nor guarantees or assurances of future performance. Important factors that could cause actual results to differ materially from those in the forward-looking statements are discussed by reference to the factors described in Part I, Item 1A “Risk Factors”, and Part II, Item 7 and Item 7A “Management’s Discussion and Analysis of Financial Condition and Results of Operations”, and “Quantitative and Qualitative Disclosure about Market Risk” in the company’s most recent Annual Report on Form 10-K and in Part I, Items 2 and 3 “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Quantitative and Qualitative Disclosures About Market Risk”, and Part II, Item 1A, “Risk Factors”, in the company’s quarterly reports filed thereafter.

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All forward-looking statements made in this report and all subsequent forward-looking statements, whether written or oral and whether made by or on behalf of the company, are expressly qualified by these cautionary statements. Any forward-looking statement speaks only as of the date on which such statement is made, and we undertake no obligation to publicly update any forward-looking statement, whether as a result of new information, future developments or otherwise, except as may be required by law. New factors emerge from time to time and it is not possible for the company to predict all such factors, nor can it assess the impact of each such factor or the extent to which any factor, or combination of factors, may cause results to differ materially from those contained in any forward-looking statements.

About NW Natural

NW Natural (NYSE:NWN) is headquartered in Portland, Ore., and provides safe, reliable, cost-effective natural gas service to about 675,000 residential, commercial, and industrial customers through 14,000 miles of mains and service lines in western Oregon and southwestern Washington. It is the largest independent natural gas utility in the Pacific Northwest. The company has approximately $2.5 billion in total assets. The company operates and owns 16 Bcf of underground storage capacity in Mist, Ore., and also operates the designed 20 Bcf Gill Ranch underground storage facility in California, in which it owns a 75 percent undivided interest. Together, NW Natural and its subsidiaries currently own and operate underground gas storage facilities with designed storage capacity of approximately 31 Bcf in Oregon and California. Additional information is available at www.nwnatural.com.

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Investor Contact:

Bob Hess

Phone: 503-220-2388

Email: bob.hess@nwnatural.com

or

Media Contact:

Kim Heiting

Phone: 503-220-2366

Email: kah@nwnatural.com

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NORTHWEST NATURAL GAS COMPANY

Comparative Income Statement

(Consolidated - Unaudited)

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NORTHWEST NATURAL GAS COMPANY

Financial Highlights

(Unaudited)

Second Quarter - 2011

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