What are the odds of rolling up the rim to win at Tim Hortons?

It's that time of year when many Canadians hope a cup of coffee could turn into a lot more.

Tim Hortons is running their annual Roll Up the Rim to Win contest, where prizes range from a free cup of coffee to brand a new car.

But what are the odds of turning your double-double into a car?

According to Tim Hortons, the odds of winning a coffee or donut are one in six and the odds of winning a car are about one in 6.5 million.

Bettina West, a professor at Ryerson University's Ted Rogers School of Management, says the chance of a reward — even if only a coffee — brings about excitement and keeps customers coming back in this very competitive environment.

"There are lots of companies out there that are happy to jump in and take their place, so it's important to keep their customers mindful and engaged and coming back," West said.

West added that by showing gratitude to customers in a way that physically engages them is also a great way to get word of mouth.

"They're rolling up rims, they're getting their fingers dirty, but the prize at the end of it is what makes it fun and it's what also creates word of mouth then as well," she said.

So how do the numbers of winners stack up across the country?

According to the company's website, the total number of Toyota RAV 4's won to date is 20 out of a possible 40. Ten of these winners were in Ontario.

Ontario's big lead in terms of the number of winners is chiefly because of the high volume of cups compared to that in other provinces.

"Of course you get to see a lot more people winning just because of the total number of cups out there," said Wei Kong Yuen, a professor of mathematics at Brock University.

There's also the issue of which cup size has a better chance of winning.

News website Huffington Post Canada found that out of 92 beverages purchased from Tim Hortons over the course of a week, larger sized drinks were more likely to roll up to a winner.

Tim Hortons customer Betty Homen agrees.

"My husband gets medium and he barely wins anything, so the larges get a lot," Homen said.

However, Tim Hortons maintains that the odds do not change depending upon the size of coffee.

Other prizes include a $5,000 prepaid MasterCard, a barbecue grill and prepaid Tim Hortons gift cards.