Petroineos’s 210,000 barrel per day (bpd) Grangemouth refinery in Scotland is preparing to re-start this weekend, three trade sources said on Friday, returning after more than a month of planned maintenance work.

The Grangemouth plant is the only major refinery in Scotland and largely processes crude oil from the North Sea.

One of the sources said most of the plant was expected to be back online by May 15.

Refinery margins in north-west Europe have weakened recently, however, limiting how much capacity the joint-venture between PetroChina and Ineos may choose to bring back into operation.

Earlier on Friday industry intelligence group Genscape said the plant’s 35,000 bpd crude distillation unit (CDU) was showing increased furnace stack activity overnight, though the plant’s other major units remain offline.

A spokesman for Ineos in Geneva declined to comment.