Oil and gas giants have accumulated $324 billion worth of tax credits in 2017-18, meaning many will not pay tax for years to come.

Australian Taxation Office (ATO) stats tax credits for fossil fuel companies operating in Australia have risen from $282 billion in 2016-17.

These credits can be used to lower liabilities in future years.

Some say it shows the petroleum resource rent tax (PPRT) is not working.

Out of 138 returns lodged in 2017-18, only six projects paid the PRRT.

This was because they received generous tax concessions for spending over a company's assessable tax receipts, which can be carried over year on year.

In 2017-18, receipts topped $29.7 billion, but only $1.16 billion was paid in PRRT.

In 2016-17, with receipts totalling more than $22.7 billion, just $970 million in PRRT was paid.

Assistant Treasurer Stuart Robert says revenue raised under the PRRT should not be compared with carry forward losses or tax credits.

“The former is a function of the profitability of projects, while the latter is a function of the money actually spent by companies to develop those projects,” he said.

“Tax losses, or credits as they are sometimes called, represent money companies have actually spent on developing projects, plus uplift, and are mostly not transferable between projects.

“As a result, the aggregated carry forward PRRT tax losses published by the ATO are not directly relevant to whether individual projects will pay PRRT.”

Greens Treasury spokesperson Senator Peter Whish-Wilson says $324 billion equates to about 70 per cent of the Commonwealth Government's total revenue.

“The PRRT is the most egregious rort in the Australian tax code,” Senator Whish-Wilson said.

“While the world is in the middle of an LNG boom, we're practically giving the stuff away.”