Diesel prices remain unchanged despite all four oil companies dropping petrol prices by 3c yesterday.

Mobil spokesman Peter Thornbury said today there had been no change, and that diesel and petrol moved quite differently.

"They are different products and have different dynamics behind them," he said.

Shell and BP also confirmed there was no change in the diesel price. Caltex was not available for comment.

Meanwhile, BP Plc in London yesterday reported a 26 per cent surge in fourth-quarter replacement cost profit to US$4.43 billion ($6.58 billion) thanks to high oil prices and strong refining margins.