LONDON (Reuters) – Greek refiner Hellenic Petroleum (HELPE) has awarded a heating oil buy tender for August to October to both Shell and Vitol, doubling its expected import volumes ahead of plant maintenance, traders said yesterday. The company, Greece’s largest refiner, tendered for two to three cargoes or up to 90,000 tons a month of heating oil, but is set to buy four to six cargoes monthly. «HELPE awarded twice for the 2-3 cargoes,» said a gas oil trader. «They always try and fill their tanks in the summer as their winter demand can be huge.» The refiner is building stocks ahead of maintenance at its 140,000-barrel-per-day Aspropyrgos plant, scheduled for a six-week shutdown from the second half of September. It is also expected to undergo maintenance at its Thessaloniki plant for 20 days in September. Refiners often have shutdowns for maintenance in the Northern Hemisphere’s fall, when gasoline demand fades and before heating oil purchase picks up. European countries are trying to increase heating oil stocks ahead of peak winter demand, with worries over low inventory levels on both sides of the Atlantic helping drive gas oil futures prices in London to all-time highs this week. «Stocks need to rise, otherwise it will cause winter problems,» a dealer said. The price level for the tender award could not be confirmed. Heating oil cargoes in the Mediterranean market were last assessed at premiums in the low teens over IPE gas oil futures on a cif basis.