Alcoa says two of its alumina refineries in Western Australia have achieved record production and remain among its lowest-cost plants globally.

Alcoa, which is closing and curtailing smelter capacity across its global operations in response to weak market conditions, has singled out Wagerup and Pinjarra in WA as being the stand-out plants in its portfolio.

Alcoa global chief executive Klaus Kleinfeld said production at the facilities rose to record levels last year while their profitability had risen by 23 per cent.

“All of that was no extra capital,” Mr Kleinfeld told a briefing on Tuesday after Alcoa posted an improvement in fourth quarter earnings.

“That’s the best thing that you can get, right?”

Alcoa also operates an aluminium smelter at Kwinana, south of Perth.

The company did not provide an update on its stalled expansion of Wagerup.

WA’s Environmental Protection Authority in February granted AWAC, Alumina and Alcoa’s joint venture company, an extension until September 2016 to substantially commence the Wagerup expansion, which was first given environmental approval in 2006.

Alumina chief executive John Bevan in February rejected a media report citing an Alcoa spokeswoman as saying the expansion would not be revisited until the joint venture had a clearer picture of the full effect of the carbon tax, due to begin on July 1.

Mr Bevan said high construction costs and the need to secure energy supplies were reasons for the delay.