Reports have emerged that Perth motorists were forced to pay more than a $1 a litre for unleaded petrol at Caltex service stations last month because the company feared it could run out of fuel.

Documents obtained by the local West Australian newspaper showed Caltex raised prices, not because of normal market forces, but to slow demand to conserve supplies.

"We were a little short in our estimates for demand in this period. As a result BP could not supply the additional amounts we wanted," Caltex Australia's manager for corporate affairs, Richard Beattie said. "It put us in a position where our services stations could have run out."

"We had to set a price that was going to reflect that shortfall because we had to be able to supply to service stations." Caltex relies on BP for petrol supplies in Perth.

However, it is believed Caltex fell short with its estimates because it won a major contract to supply Woolworths late last year and was obliged to maintain supplies.