PUMP prices fell on Thursday after crude oil tumbled below US$140 a barrel on Tuesday.

Petrol rates dropped by four cents a litre while diesel slid by two - just a week after the first reduction in 18 months.

A litre of 92, 95 and 98-octane petrol now costs $2.173, $2.206 and $2.28 before discount. So-called ultra-premium grades, Shells' V-Power and Caltex's Platinum, are now $2.399 and $2.396 respectively.

Diesel is $2.013.

The lower rates followed swiftly the plunge in crude prices, when news broke early this week that the US had larger oil reserves than expected.

Industry watchers noted that pump prices seem to be moving more closely in tandem with oil prices in recent months.

Consumers Association of Singapore executive director Seah Seng Choon said: 'Consumers will welcome such quick response on the part of the oil companies. We believe oil companies are able to adjust pump price promptly and the latest move shows that such action is possible.'

Compressed natural gas (CNG) prices, meanwhile, have been rising sharply. They are now over 40 per cent costlier than six months ago.

With this, the gap between CNG and petrol has narrowed considerably.

Today, a kilogram of CNG is about 35 cents cheaper than a litre of petrol. The difference was 70 cents as recently in February.