The G20 meeting starting today in Seoul will not sign off on the final Basel III regulatory regime, with a key clause affecting Australia still to be fixed.For Australian banks, the sole remaining issue in the Basel III discussions is how planned liquidity ratios will be dealt with in Australia and other countries (Singapore, Hong Kong and Saudi Arabia among them) whose low debt means the likely future supply of government bonds is limited.There have been reports in recent months that this issue and others could be decided in time to have the Basel III package endorsed at the G20 summit.But Banking Day understands that the issue is one of several still being debated in sub-committees of the Basel Committee on Banking Supervision, the key global forum on banking supervisory matters.The G20 is instead expected to declare high-level agreement on the Basel III package, with details to be finalised over the next three weeks.The New York Times reported European Central Bank president Jean-Claude Trichet as saying the rules were "a work in progress", with a lot of fine-tuning still needed.The final package is now likely to be released at the two-day Basel Committee meeting, starting on 30 November.Meanwhile, it has been confirmed that the Basel III package will define "systemically important banks" in a way that will leave the Australian prudential system untouched.The Financial Times reported on Wednesday that officials had concluded that the treatment of "systemically important banks" should focus on big banks with global businesses.An alternative definition would have included all banks that are systemically important to a national or regional market, which could have included Australia's Westpac, CBA, NAB and ANZ.The chosen definition leaves APRA free to set the rules for the Big Four.