While many locations across the country have seen prices below that mark for a couple of weeks, Thursday was the first time since Aug. 30, 2010, that the average dipped to 99.9 cents.
In a statement, the website operator says Thursday also marked the 77th consecutive day that the national average has declined.
GasBuddy says average prices are about 28 per cent below the peak of $1.39.3, reached on June 22.
To put that in perspective for the average motorist using 80 litres of gasoline per week, the savings between the June peak price and Thursday's average works out to between $35 and $40 weekly.
The milestone may be short-lived, however, as prices are expected to increase by up to two cents per litre in many parts of the country by Friday.
GasBuddy senior petroleum analyst Dan McTeague says it's anyone's guess where prices will go next.
Alberta typically enjoys the lowest fuel prices in the country. The province's average pump price currently sits at 88.1 cents.
Edmonton residents, meantime, are experiencing the lowest average prices by metropolitan area, at 81.8 cents.
Quebec motorists are still paying more than $1, with the average cost of a litre of regular in Montreal and Quebec City down to 109.5 and 108.4 cents respectively.
The price difference from one part of the country to another largely comes down to the tax regimes adopted by governments, says McTeague.
"A lot of it has to do with taxes," he said.
"In fact if you look at the wholesale price of gasoline in Montreal and the wholesale price in Calgary or in Edmonton, you'll find they're about the same. The real, major difference there, unfortunately, is taxation."