By Justin Scheck 

LONDON-- Royal Dutch Shell PLC said second-quarter earnings more than doubled from a year earlier as the Anglo-Dutch oil and gas group benefited from higher production of liquid petroleum and higher prices for certain products.

Shell said Thursday that profit for the period came in at $5.15 billion on a current cost-of-supplies basis--a measure similar to profit reported by U.S. oil companies--compared with $2.39 billion in the same period last year. Excluding one-time items, current-cost-of-supplies profit was $6.13 billion, up 33% from $4.60 billion last year.

Second-quarter sales were $115.27 billion, up slightly from $114.35 billion a year earlier.

"Our financial performance for the second quarter of 2014 was more robust than year-ago levels but I want to see stronger, more competitive results right across the company," Chief Executive Ben van Beurden said in a statement.

Shell recorded impairment charges of $1.94 billion, largely related to U.S. shale assets, an area where Shell and other big companies have struggled to profit as smaller companies have sparked a natural-gas boom. Mr. van Beurden said Shell's onshore shale and so-called "tight" oil and gas business--which targets resources trapped in underground rock--lost some $400 million in the first half of 2014. The company is in the process of restructuring the North American shale business.

"They've obviously made some bad-value decisions in the past, and they're getting them out of the system," said Jason Kenney, an analyst at Banco Santander who covers oil companies. He called the second-quarter results "encouraging."

Mr. van Beurden said a joint-venture between Shell and Russia's Gazprom Neft includes a shale project that could be subject to new sanctions levied by the European Union and U.S. in response to the fighting in Ukraine. The sanctions restrict exports of technology to Russia for extracting oil from the Arctic, deep sea and shale. But Mr. van Beurden said it isn't clear how the project will be affected.

Oil and gas production during the quarter was 3.08 million barrels of oil equivalent a day, about the same as a year earlier.

Since taking over as CEO in January, Mr. van Beurden has promised to improve profitability at the sprawling company.

In its exploration-and-production, or upstream, division, Shell reported earnings of $3.82 billion, up from $1.68 billion a year earlier. Excluding one-time items like write downs, upstream earnings were $4.72 billion for the quarter, up from $3.53 billion in the prior period. Shell said the division benefited from increased production in the U.S. Gulf of Mexico and Iraq, as well as increased shipments of liquefied natural gas from a facility Shell bought earlier this year.

Profit in Shell's refining, or downstream, business was $1.27 billion, up 58% from a year. Excluding one-time items, profit was up 15%, to $1.35 billion.

Shell reported a dividend of 94 cents per American depository share, up 4% from a year earlier.

Write to Justin Scheck at justin.scheck@wsj.com

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