Drivers might want to fill up their tanks before Wednesday morning.

This is when gas prices in Waterloo Region are expected to increase by four cents a litre.

The reason for the fuel increase: an attack on a Saudi Arabia oil processing plant on Saturday.

A rebel group based in Yemen and backed by Iran is taking responsibility.

The led to fires and cut off millions of barrels of crude oil supplies from the world's largest oil exporter.

Petroleum analyst Dan McTeague says the price depends on when the oil goes back online, or whether or not there is military response.

"The reality I think for most is that we live in a very dangerous situation," he said. "Ouf course it could lead to much higher prices among other things."

Until then, McTeague expects the cost of fuel will rise and drop rapidly until mid-October.

“It’s going to be a very volatile time between now and Thanksgiving,” he said.

The analyst adds the increase won’t be higher than four cents because Canada switched to its winter blend of gasoline one day before the attack.

“We dodged a bullet,” said McTeague.

A winter blend of gasoline is cheaper to produce and typically four cents less than the summer blend.

The summer and winter blends do not apply to diesel fuel. It is expected to see an eight to nine per cent per litre increase.