This made ChevronTexaco and Flint Hills Resources the only suppliers to refrain from double-digit increases. Observers speculated that those two Group II producers may have been following Motiva, which cut its prices in relation to other Group IIs during the summer. Motivas actions were also credited for ConocoPhillips decision to forgo the previous round of increases, which occurred in late August and early September.

Paraffinic posted prices have risen by approximately 20 percent since the start of the year, and observers said they will almost certainly continue to climb as long as crude keeps moving upward. Indeed, buyers and sellers suggested that base oils still have not caught up to crude and could increase further even if crude levels off.

[Base oil] margins are definitely down from a year ago, one buyer noted. I think [pricing leader] ExxonMobil will do what it needs to do to restore margins.

The cost of crude on the New York Mercantile Exchange climbed as high as $54.45 per barrel yesterday, before slipping back to close at $52.51. The closing price was $1.52 higher than a week earlier.

Analysts said the latest surge was caused by concerns that supply disruptions from Hurricane Ivan will tax the oil industrys ability to meet heating oil demand this winter. But some analysts contended that such worries were overblown, given the relatively small size of the heating oil market. Hence, they said, the retreat from Tuesdays peak prices.

Historic U.S. posted base oil prices and WTI and Brent crude spot prices are available for purchase in Excel format.