E.ON Ruhrgas AG, Germany 's largest importer of natural gas by volume, said Thursday it plans to auction 55 terawatt-hours of gas over a five-year period.

The auction, which is targeted at gas sellers, traders and financial institutions as well as large industrial customers and municipal utilities, will begin in August, the company said in an emailed statement.

It said it will offer 11 TWh a year, divided into 220 lots of 50 million kilowatt-hours a year.

Customers can choose between two pricing mechanisms, E.ON Ruhrgas said. In the first the price of the gas deliveries will be linked to crude oil prices, while in the second prices will be determined by a combination of oil and spot gas market prices.