Scientists at the Max Planck Institute for Chemistry in Mainz, Germany, carried out extensive tests along nearly 2,400 kilometers (1,500 miles) of Russian gas pipelines and pumping stations.

They estimate that the overall leakage from the system is 1.4 percent, "considerably less than expected" and even better than the 1.5 percent loss that occurs in the US natural gas system.

A study published by Russian scientists in 2000 had suggested that as much as 10 percent of Russian gas could leak out during production and transport.

The latest research, published on Thursday in Nature, is significant because many European countries are facing important choices in their energy strategy.

They are required under the UN's Kyoto Protocol to meet targets for fighting global warming yet must also meet domestic energy needs, and Russian gas is a leading option.

Burning natural gas, which is 90-percent methane, in power stations and in homes causes less carbon dioxide (CO2) pollution per unit of energy yielded than oil or coal.

On the other hand, methane is itself a big greenhouse gas.

The worry has been that European countries which import Russian gas as an energy substitute may in fact be helping global warming if lots of this gas escapes into the atmosphere on its way from Siberia.

Volume for volume, methane is up to 22 times more efficient than CO2, by far the biggest greenhouse gas, in trapping heat from the Sun.

However, that measurement applies to a timescale of 20 years.

When measured over a century, the efficiency factor falls from 22 to eight because CO2 lingers longer in the atmosphere than methane, which is more swiftly degraded and absorbed by Earth's biosphere.

If methane is burned, that still contributes to global warming because the combustion process releases CO2.

Thus natural gas is only a temporary solution, helping the switch from dirtier oil and gas, and not the answer to the carbon pollution problem itself.

According to the new study, methane can carry out this stop-gap role but only provided methane leakage into the atmosphere "is below about three percent."

Russia has gas reserves estimated at 47,000 billion cubic metrestrillion cu. feet).

It extracts 580 billion cu. metres of gas (20,300 billion cu. ft.) per year -- around a fifth of global production -- of which 115 billion cu. metres (4,025 billion cu. ft.) gets pumped to countries of the European Union.

The United States is the second biggest producer, with 550 billion cu. metres (19,250 billion cu. ft.) per year.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.