The plunge in commodity prices has sent Woodside Petroleum's first-half profit down 50 per cent, but chief executive Peter Coleman said the oil and gas producer was in a "robust" position as oil price forecasts improve into 2017.

Bottom line profit for the six months to June 30 fell to $US340 million, shy of analyst consensus forecasts. RBC Capital Markets blamed the shortfall on a loss on LNG trading, foreign exchange and tax.