The deal between Kansai Electric Power and BP is the first contract in Japan to be linked to gas rather than oil prices. BP will supply 500,000 tonnes per annum from Egypt and Trinidad and Tobago under the deal, set to begin in 2017.

Kansai says it believes the contract will be 30 per cent cheaper than an equivalent one linked to oil prices.

The move sounds a grim warning to Australian suppliers, who are already battling cost pressures and are dependent on the fat profits from selling gas to Japan under the oil-linked pricing regime, in which overall exports hit $11 billion last financial year.

While Australian producers have tried to play down the threat posed by the shale boom and the pressure to change the pricing system, analysts have warned that the more costly projects in Australia's $200bn liquefied natural gas pipeline were becoming increasingly vulnerable.

And a leading resource lawyer has warned that Japanese buyers of Australian LNG would "no doubt" try to renegotiate their contracts with suppliers in the current environment, although those for existing projects appear to be solid.

Analysts in Tokyo said more deals could be struck at the US (Henry Hub) price, and Japan - the world's largest buyer of LNG and Australia's biggest LNG export market - would eventually try to establish this pricing mechanism for Asian LNG sales from Australian fields and elsewhere.

Korean utilities are pushing for a new pricing model reflecting the US price rather than the oil price. Utilities have previously bought their gas at a price linked to the Japanese Crude Cocktail, essentially the oil price, but prices struck on this basis are now about four times as high as Henry Hub.

Even accounting for shipping and liquefaction, Japanese figures suggest a saving of more than 30 per cent on US gas landed in Tokyo, versus Australian gas.

The demand for gas in the wake of the Fukushima crisis, which has seen almost all of the country's nuclear power plants shut down, has seen the power companies post huge losses. As a result, they have been pushing for the US gas price, currently at about $3.50 per million British thermal units because of the shale gas boom, to be the key determinant for pricing. The shale boom is attracting much interest in Australia, led by BHP's massive investment. Woodside boss Peter Coleman last week said his company was looking at opportunities in the US.

Japan is hoping to secure permission from the US soon to be eligible for export gas shipments, a privilege Washington generally reserves only for countries with which it has free trade agreements.

Tokyo analyst Reiji Ogino, of Morgan Stanley MUFG Securities, said the utilities' hope was "to increase the number of long-term contracts based on the Henry Hub price as soon as possible".