By Martin Cassidy BBC Northern Ireland rural affairs correspondent

Most of the fuel comes from a volatile Middle East

In the past, farmers have been militant protesters, but rather than taking to the streets they are now striking oil themselves and cashing in on a lucrative market for fuel.

Five years ago, it was farmers who helped lead the fuel price protest in Belfast with tractors and combine harvesters pulling up at the steps of Parliament Buildings at Stormont.

Now though, it is a very different story with a growing number of farmers planting oilseed crops to produce bio-diesel.

Frustrated by falling produce prices, the Ulster Farmers' Union believes fuel production represents a major opportunity for its members.

The union's chief executive, Clarke Black, sees a new role for farmers.

Michael Harnett's oilseed crop is already safely stored

"The technology is being refined and there is no doubt it is possible to grow crops that will produce oil that can be refined into fuel that can run in most cars," he said.

Not far from the farmers' union headquarters on Belfast's Antrim Road, motorists queue for petrol and diesel priced at just under �1 per litre.

Most of the fuel at this forecourt and across the country comes from a volatile Middle East.

But OPEC now has competition from farmers who are quickly developing local oil producing capacity.

Michael Harnett from Waringstown in County Down may seem an unlikely oil prospector, but his oilseed crop is already safely stored in the grain silos which look down on this picturesque farmyard.

Michael Harnett's oilseed crusher is working flat out

Picking up a handful of the black oilseed rape, Michael Harnett explains how a crop grown in nearby fields has the power to drive cars and lorries.

"Oilseed rape is up to 46% oil. That means for every tonne of this oilseed there is almost half a tonne of oil - that's 520 litres from a tonne of seed," he said.

Given current fuel prices, farmers see oilseed crops having the potential to earn up to �1,000 an acre.

Not bad for a crop which can be grown in fields which must be left fallow under EU setaside rules.

Such is the potential of bio-fuel, that Ireland already has one refinery and another is planned.

Mindful though of their experiences with food processors and supermarkets, farmers are getting involved in refining themselves.

Oilseed rape has the power to drive cars and lorries

Michael Harnett's oilseed crusher is working flat out. The oilseed rape is pressed though an extruder which separates the oil from the cake, which then goes for livestock feed.

More than 1,500 tonnes of oilseed rape will be refined on his farm this year.