The two West Australia power firms signed supply contracts on Wednesday with gas suppliers. The deal would boost gas security for residents.

State-owned power station operator Verve Energy and energy retailer Synergy inked the agreements with Chevron's $43-billion Gorgon liquefied natural gas (LNG) project and joint venture partners ExxonMobil and Shell.

The agreement assures 125 terajoules per day supply of LNG sufficient for 20 years. The deal takes effect in 2015, which would coincide with the end of Verve's and Synergy's current gas supply contracts.

"The reaching of these agreements provides long term and reliable domestic energy supply, which will enable us to maintain a strong and vibrant economic in conjunction with an additional stream of gas security," WA Energy Minister Peter Collier said in a statement.

Mr Collier admitted the two contracts would lead to higher electricity prices because the old contracts were cheaper than the new ones. While he could not provide an estimate on how much power costs would increase, the minister promised to keep adjustments to a minimum.

However, Labor leader Eric Ripper said West Australia residents could not afford to pay higher electricity prices.

Gorgon will start to supply West Australia LNG in 2005 under the state's 15 per cent domestic gas reservation policy.

Chevron is slated to ground break on Thursday the $29-billion Wheatstone joint venture with Apache Energy, Shell and KUFPEC of Kuwait, also located in WA.

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