Mr Carpenter's Government was thrown out of power on Sunday after the Nationals chose to support the Liberals in the state's hung Parliament following the state election held on September 6.

Yesterday, the Nationals released the written submissions by both Mr Carpenter and Premier-elect Colin Barnett to WA Nationals leader Brendon Grylls.

In his letter, Mr Carpenter offered an annual $1billion Royalties for Regions package for investment in regional services and infrastructure.

The offer was worth substantially more than the Nationals' demands on both Labor and the Liberals for 25 per cent of mining royalties over four years, worth an estimated $675million a year.

Mr Barnett said his offer to Mr Grylls on royalties for regions was the $675million annual amount cited by the Nationals as the starting point for all negotiations.

Mr Carpenter's letter to Mr Grylls said Labor's offer would keep the state's net debt-to-revenue ratio below the 47 per cent needed to maintain the state's AAA credit rating.

Labor also offered the Nationals responsibility for agriculture, as well as development, transport, housing, power, education and health in the regions, worth $2.7billion in projects and services.

Mr Grylls said on Sunday that one main reason the Nationals did not choose Labor was because the Greens would have held the balance of power in the upper house, reviewing all Nationals legislation.

The Nationals leader met Mr Barnett yesterday to begin discussing the structure of their arrangement, including the allocation of portfolios.

Mr Grylls will be minister for regional development, overseeing the Royalties for Regions fund.

Mr Barnett said his cabinet would be larger than the 14 ministers under Labor and could be sworn in by Friday or early next week. AAP