CALGARY -- Plunging world oil prices have delivered a Christmas miracle of lower gasoline prices across most of Canada but a fuel price expert says motorists should fill up now because prices are expected to be volatile in 2019.

Dan McTeague, a senior petroleum analyst at GasBuddy.com, says gasoline prices are at near-18-month lows because of global oil prices that have tumbled over the past two months on worries of an economic downturn, a U.S.-China trading tiff and concerns that members of the OPEC oil cartel won't live up to production cuts.

Despite a brief oil price rally on Wednesday, average regular gasoline prices remain about 17 cents lower per litre than a year ago in Alberta and Ontario, 12 cents lower in Manitoba, six cents lower in Quebec, 11 cents lower in Nova Scotia and three cents lower in Newfoundland and Labrador.

McTeague says prices in B.C. are up two to six cents per litre compared with the same time last year but would be lower if not for the effect of interruptions in fuel imports from Washington due to the outage of that state's Olympic Pipeline in mid-December.

U.S. benchmark West Texas Intermediate oil prices plunged to US$42.53 on Christmas Eve, down 44 per cent from US$76.41 per barrel on Oct. 3. They rallied to US$46.22 on Wednesday but trended lower Thursday.

McTeague says "extreme volatility" in oil markets are expected to continue to wreak havoc on gasoline prices in Canada in the early part of 2019.

"I think what we're seeing here where oil prices -- and pump prices as a corollary -- are going up and down five and 10 per cent in a given week, much of this is really a harbinger of what we're likely to see in 2019, extreme price movements," he said.