US naphthenic base oils output rose in April, contrasting with a fall in production of paraffinic supplies.
Naphthenic base oils output of 822,000bl in April rose by 18pc from 697,000bl in March to a seven-month high, government data showed.
The increase contrasted with a drop in paraffinic base oils production to 4.07mn bl in April, from 4.47mn bl the previous month.
The contrasting trends likely reflected the different timing of plant maintenance work, with most naphthenic plant maintenance taking place earlier in the year.
Strong middle distillate prices and relatively weak base oil prices relative to crude and diesel earlier in the year also incentivized refiners with paraffinic production to boost output of diesel and jet fuel.
By contrast, naphthenic base oils prices tend to have a more direct link with crude oil prices, cushioning more the effect on margins of the rise in crude and diesel prices since early this year.
The higher naphthenic base oils output in April mostly reflected a jump in production in the US Gulf coast region to an eight-month high of 707,000bl, from less than 600,000bl the previous month.
The rise in production boosted the share of naphthenic base oils output to 16.8pc of total US base oils production in April. The share was up from 13.6pc in March and the highest in more than a year.