FACTBOX: Why is Nigerian oil militant attack significant?

(Reuters) - Militants in speedboats attacked Royal Dutch Shell's main offshore facility in Nigeria on Thursday.

Below are answers to some questions about the attack and what it could mean:

WHY IS THIS ATTACK DIFFERENT?

Militant attacks on oil installations in Nigeria have mostly targeted facilities in the shallow creeks of the Niger Delta, where pipeline bombings and kidnappings of expatriate oil workers have been frequent.

Thursday's attack targeted Shell's Bonga oilfield, which lies some 120 km (75 miles) off the Nigerian coast.

Such offshore facilities have been considered safer and easier to protect and attacks of this kind have been relatively rare. International oil companies have been focusing investment offshore partly because of the perceived lower risk.

HOW ARE WORLD OIL PRICES AFFECTED?

Global oil prices are already near record highs above $130 a barrel. With the bullish sentiment already in the market, news of any supply disruption in a major oil-producing country will spark further buying.

Militant attacks and a workers' strike in late April slashed more than half of Nigeria's production, helping oil prices surge to a then-record $120 a barrel.

Nigeria's sweet crude is popular with U.S. and European oil companies because it can be easily refined into gasoline, diesel and other products. The oil is sold at a premium to benchmark U.S. and European crudes.

HOW WILL THE INDUSTRY BE AFFECTED IN THE LONG TERM?

Attacks on oil facilities in the Niger Delta have depressed Nigeria's oil output by a fifth since early 2006, but oil companies had hoped that increasing offshore production would help to make up for the shortfall.

A sustained campaign of sabotage against offshore installations could prevent those newer projects from reaching their full potential and leave Nigeria struggling to meet its OPEC quota.

The banks financing the oil industry had thought that offshore projects were a safer bet, being relatively insulated from militant attacks. The cost of financing such projects may increase if that turns out not to be the case.

WHO ARE THE REBELS?

The Movement for the Emancipation of the Niger Delta (MEND) claimed responsibility for the attack. It is a nebulous organization which emerged in late 2005 and says it is fighting for local communities to gain greater control of oil resources.