South Korean refiner Hyundai Shell Base Oil (HSB) saw its profit rise in the third quarter from the previous three months to its highest in a year as sales rose faster than costs.But profit fell from year-earlier levels for a third straight quarter.The joint venture between Hyundai Oilbank and Shell saw operating profit rise to 50.4 billion South Korean won ($35.5mn) in the three months to end-September.Profit rose by 71pc from W29.4bn during the second quarter of the year.Profit rose as a 35pc rise in sales from the second quarter outpaced a 32pc increase in costs..Record-high sales of W388.7bn got a boost from unusually high outright base oils prices compared with historic levels.Asia-Pacific Group II base oils prices edged down by 3pc in the third quarter of the year from the previous three months. Even then they remained close to their highest levels in years and up more than 10pc from year-earlier levels.Scheduled plant maintenance work impacted HSB’s base oils supply in the second quarter of the year. It had no such maintenance work in the third quarter.With sales rising faster than costs, HSB’s operating profit margin recovered to 13pc in the third quarter, up from 10.3pc during the previous three months.Last year’s quarterly profit margins were unusually high because of similarly high base oils prices but much lower crude oil feedstock costs.Excluding last year, the profit margin was above its long-term average of less than 10pc. It also rose above Hyundai Oilbank’s refining profit margin for the first time this year.HSB’s profit margin recovered even amid unexpectedly weak Chinese demand and a persistent supply overhang in the Asia-Pacific market during the third quarter of the year..S Korea refiner HSB’s Q2 profit up vs Q1