Top global gas shippers, converging on Rome this week, face renewed uncertainty over falling prices after reaping handsome profits this year as prices jumped following Japan's Fukushima nuclear disaster and due to unrest in the Middle East.

But the new prospects for the liquefied natural gas (LNG) sector due to an inflow of fresh U.S. supply, following last month's $8 billion (5 billion pound) deal between Britain's BG Group and Cheniere Energy , is likely to be a major topic at the industry gathering.

The World LNG Summit in Rome opens on Tuesday and runs until Thursday. Effectively this is an LNG pre-Christmas bash but early this year, one senior LNG trade source said.

Cargoes of LNG are changing hands for up to $50 million each and cash is gushing in.

With oil prices high, LNG sales into Asian markets have boosted trading profits at BG Group, Royal Dutch Shell , Total and GDF Suez , not to mention state-backed firms such as Qatargas and Nigeria LNG, which tie long-term gas supplies to a barrel of crude oil.

Japan's nuclear crisis due to an earthquake in March fuelled a remarkable transformation in the global LNG trade, quelling doubts about the fate of a fledgling spot market that many said would fade from view.

Japan, the world's third largest economy, substituted atomic energy with gas after the Fukushima Daiichi plant meltdowns.

Asian gas prices have rocketed more than 50 percent since March, adding to bumper profits for traders.

PRICE DROP

Despite the backslapping and celebrations, traders will be keenly aware that the engine which has driven spot LNG prices ever higher is in reverse.

In the last month, softer Asian demand has wiped more than $1 per million British thermal units (mmBtu) off spot prices, to about $17/mmBtu -- a trend some say will continue.

Poor power demand that has approached annual lows has preserved stockpiles of LNG held in terminal tanks, cutting competition in the world's biggest market.

This may be a short-term glitch caused by unusually mild weather in the region.

With LNG demand still comparatively high, the scramble to pin down new supplies has prompted the industry to innovate and accept risk.

Last month's landmark deal between BG Group and Cheniere Energy to export bountiful U.S. shale gas supplies to the world for the first time, looks set to turn the tide of the LNG business, analysts and traders say.

It paves the way for terminal developer Cheniere to secure financing for the its Sabine Pass project in Louisiana which could be the first LNG export plant built in the United States in nearly 50 years as U.S. gas production hits record highs.

But the deal also implies a big gamble on the future oil-gas price spread, which ultimately will seal the project's fate, one way or the other.

Provided U.S. gas prices maintain heavy discounts to crude oil, exports will reap massive margins. If the spread reverses, the economic incentives vanish, with Cheniere and BG taking the hit.

Despite the risks, further export agreements are in the pipeline, with French major Total touted as a leading contender for an export deal with Cheniere, sources say.

Terminal developers such as Cheniere are scrambling to turn their idle import facilities into export plants to ship U.S. natural gas abroad after the revolution in shale gas production left the United States with 100 years of supply.

BG Group, one of the world's biggest LNG players, has access to import markets across the globe. Anywhere from Japan to Korea to Chile could soon be importing U.S. gas.

(Reporting by Oleg Vukmanovic; Editing by Jason Neely and Anthony Barker)