According to the Interstate Natural Gas Association (INGA), thirty pipelines, mostly underground and located in every US state, transports about 90 per cent of the natural gas in the US. Since September 11, the energy industry has stepped up security measures especially at above-ground compressor stations.

"Gas companies continue to monitor and patrol the pipelines regularly via aircraft, vehicles and also by foot," INGA said.

As for Australia, a Woodside Petroleum spokesman said the energy giant operates a national asset and the September 11 attacks has heightened the state of awareness across the assets. Some in the media have speculated that the Royal Australian Navy has increased its surveillance activities around North West Shelf Assets in the wake of the attacks.