In an unusual move, Singapore Petroleum Co (SPC) has kept its pump prices unchanged since May 6, bucking a trend which saw all other pump operators here raising prices a week after the last downward adjustment.

The Chinese-owned firm's pump prices before discount remain the lowest, with 98-, 95-and 92-octane petrol at $2.33, $1.99 and $1.95 per litre. Its diesel is $1.64 per litre.

All others, led by Esso on May 18, have raised prices which are three to eight cents per litre higher than SPC's. The increase came a week after an across-the-board cut.

SPC was unable to say how it could keep its rates unchanged even as wholesale petrol prices have been trending upwards since late last month.

Queried by The Straits Times, an SPC spokesman said: "At SPC, we monitor the market closely and periodically review and adjust pump prices, as well as promotions, to reflect prevailing market conditions.

"SPC has always offered competitive pricing for our petrol and diesel products and will continue to do so."

Oil industry consultant Ong Eng Tong, however, said the PetroChina-owned company was able to deviate from other pump operators because it now has its own direct source of fuels.

"It no longer has to depend on other oil companies like previously," he said, adding that as a Chinese company, it wants to assert its presence among "the Western companies... especially now".

The other Chinese operator here - Sinopec - is unable to do likewise because it gets its supplies from Shell, Mr Ong said.

Usually, pump operators will all adjust prices within days of one another. SPC's stance, though unusual, is not its first. Early this year, it also resisted a round of price increases which saw all the other players raising petrol and diesel prices by three cents a litre from Jan 6.

Within a week, the other players reverted to their previous rates.

SPC's rates are now the lowest fuel prices have been since 2015, before government petrol duty was raised.