Refinery margins – the profit from processing crude oil into jet fuel, diesel, gasoline and other products – have been unusually high since oil prices started a sharp decline in June last year, offering badly needed support to the world's top oil companies.

The strong run has led several operators to delay works in recent months, traders and analysts say, but many refineries are unable to postpone essential repair and upgrading work scheduled in many cases years ago.

"If (refiners) can, they would delay. But it is very difficult, for example, for a company like us", said Matti Lievonen, chief executive of Finnish refiner Neste Oil, whose 206,000 barrels per day (bpd) Porvoo refinery will shut for an 8-week maintenance in April.

"We will have very big maintenance with more than 4,000 people, which we planned over the last five years. But if you have maintenance on a smaller unit and if the authorities give the approval to extend that period, then they can do it."

Overall maintenance for March is expected to account for a roughly similar amount to 2014 at 1.10 million bpd, according to estimates by Vienna-based JBC Energy, whose nameplate capacity for the region is 15.68 million bpd.

April will be significantly lower at 1.03 million bpd compared with 1.56 million bpd a year earlier.

Most of the turnaround between March and May will take place in northwest Europe. For March, 635,000 bpd of capacity is expected to go offline, more than double levels removed a year earlier.

Industry monitor IIR Energy says 599,000 bpd of crude distillation units (CDU), which are the primary refining units, will go down for works in March, compared with a five-year average of 1.05 million bpd. IIR's nameplate capacity for 2015 is 14.23 million bpd for northwest Europe and the Mediterranean.

For April, 385,000 bpd of CDU capacity will be offline compared to a 1.02 million bpd 5-year average, according to IIR.

Maintenance includes Germany's 310,000 bpd Karlsruhe refinery, Phillips 66's 234,000 bpd Humber refinery in England and the hydrocracker at PetroIneos' 240,000 bpd Lavera refinery in France. [REF/E]

RUN, RUN, RUN

Refinery margins were more than $5 per barrel higher in January this year compared with 2014, when they were at minus 30 cents a barrel, according to JBC.

European refining margins in the first quarter of 2015 are expected to average $4.25 a barrel, compared with $1.50 a barrel a year ago. Second quarter margins are forecast to average $3.40 a barrel this year, compared with $2.60 a barrel last year.

"In the first part of this year, refineries were running close to flat out," said JBC analyst Michael Dei-Michei. "Everyone who could run, and sell their barrels, did."

Continued demand from Latin America, freezing temperatures in the U.S. East Coast and strikes at 12 U.S. refineries are expected to prop up margins in the coming months, albeit at lower levels than seen earlier this year.

"We're more positive on margins these days ... Inland stocks are low and exports from the U.S. Gulf Coast will be limited due to good U.S. and Latin American demand and turnarounds there," said Robert Campbell, analyst at Energy Aspects.

(Additional reporting by Himanshu Ojha, editing by David Evans)

By Ron Bousso and Libby George