Shell's floating LNG project had expected a decision from Environment Protection Minister Peter Garrett on April 30 but it was pushed back because the federal Department of Environment, Water, Heritage and the Arts needed more information about the project's greenhouse gas emissions.

Now another delay, this time until the end of July, has raised questions about whether Mr Garrett is dithering or exercising due care in granting environmental approval.

Santos and BG were given an additional three months to provide information on their separate plans to build LNG projects on Curtis Island in Gladstone.

Mr Garrett issued the extension amid concerns by Queensland's Coordinator-General and local communities about the companies' water management strategies and a potential threat to the Great Artesian Basin.

A spokeswoman for the Environment Department said Shell's Prelude project was complex, and that this was the first environmental assessment of a floating LNG proposal in Australia.

''This is brand new application of LNG technology, and therefore the assessment of its potential environmental impacts is not something that can be rushed,'' she said. ''It's not unusual to extend decision due dates for projects that require a thorough understanding of new approaches or technology that have not previously been assessed under national environmental law.''

Opposition environment spokesman Greg Hunt said it was ''inconceivable that so many projects are subject to delay''.

''This is the second major project delay that has come to light in two days,'' he said.

Shell is hoping for a final investment decision by early 2011, with a view to producing in 2016.