WASHINGTON (AFP) - One month into its unrest, the shutdown of Libya's oil fields is creating strains in the world's oil networks as consumers scour the world to replace its highly-prized "sweet" crude. With strongman Moamer Kadhafi entrenched and the conflict with rebels raging on, producers see no quick return to the market for Libyan crude. That is sparking a search for reserves elsewhere in Africa and around the globe. On paper it should be easy to substitute Libya's 1.7-million-barrel a day production, which meets only two percent of worldwide demand. Oil hyper-power Saudi Arabia has even offered to pump enough to match the Libyan shortfall. But oil markets worry about quality as well as quantity. Libya's low-sulfur "sweet" crude is much prized for being easy and cheap to refine into petrol. Much of Saudi Arabian crude is lower quality and more difficult to refine. "It's forcing people to look at what their options are going forward, because it now looks clear that Libya supply might be disrupted for some time," said Bhushan Bahree, an oil analyst with IHS CERA. Unfortunately, finding crude of the same quality is not easy. Only a handful of suppliers fit the bill. "The crudes that would be very similar would be Algeria, Angolan and Nigerian. None of them are exactly the same, but they are very similar," said Bahree. Demand for those crudes has surged since the crisis began, forcing up prices. Nigeria's top contract "Bonny Light" and Algeria's "Saharan Blend" are now being listed, respectively, at a $3.40 and $2.85 per barrel premium over London's main contract -- roughly double the premium in mid-February. "Nigeria is pumping all they can" to meet demand, said oil analyst Mike Fitzpatrick of the Kilduff Report, who noted Nigeria itself is far from stable. The economics of refining make it difficult to decide if that premium is worth paying. Until now oil analysts believe the true extent of the shortfall has not been realized, because many refineries are content to use up stockpiles. Others are closed as they retool to take lighter grades that are in high demand in the northern summer. "It is very complex economics that is going on at the refiners," said Bahree. Eventually many refineries will have to decide whether it is worth switching production to harder-to-refine, and less profitable, blends. If the crisis is prolonged "it could conflict with a seasonal ramp-up in refinery production ahead of the peak summer driving season," the US Energy Information Administration warned in a recent review of the oil market. No matter what the technical or logistic fixes, the cost of producing oil looks likely to rise at a time when it would have the most devastating impact. Since protests began in the rebel stronghold of Benghazi in mid-February, crude oil prices have soared -- along with prices at the pump -- prompting fears that the global recovery is under threat. Crude prices have risen by about $15-$20 a barrel, depending on where the crude is bought. US consumers are paying roughly 12 percent more for petrol and German consumers pay closer to 16 percent more. One top US Federal Reserve policy maker this week described rising energy costs as "a key risk" to the global economy. The price rises also come at a time when three of the four pillars of that normally prop up the global economy are looking decidedly wobbly. Japan is dealing with a devastating earthquake, tsunami and nuclear crisis; Europe is weighed down in a debt crisis and slow growth and US consumers are struggling with high unemployment. Higher oil prices could shave half a percentage point off growth in the world's advanced economies by 2012, according to the Organisation for Economic Cooperation and Development. Libya's political crisis could yet prompt a global economic crisis thanks, in part, to the vagaries of geology, engineering and logistics.