"This is a major refinery maintenance, and it was initially planned for April. But the maintenance was later finalised to take place in early May," said a trader.

The plant is expected to resume operations around May 22.

The refinery has a crude intake capacity of 47,100 barrels per day (bpd), and it houses a 500-tonne per day platformer -- a gasoline-making unit -- among other secondary units, data from its website showed.

Pakistan is net short of gasoline and relies on imports to plug shortfalls. It the second-half of April, Pakistan bought 285,000 tonnes of gasoline for May to September arrival.

But it exports naphtha, with PRL having recently sold 10,000 tonnes of paraffinic naphtha for May 7-9 loading from Karachi at premiums of about $20.00 a tonne to Middle East quotes on a free-on-board (FOB) to Total.