Oral contracts do exist, and they are still used. When someone promises goods or services in exchange for compensation—money, typically, though other types of compensation may be used—the person then has to follow through on it. However, though you may be tempted to use these because they're easy and they save you some time, it's always better to get everything in writing.
This way, if there is ever a disagreement about what was laid out in the contract, you can refer to it. You can take it to court and show it to the judge, if need be. You don't have to worry about convincing anyone that you're right, because you have the proof right in front of you.
With an oral contract, there's no guarantee. You may both remember the events differently. You may claim one thing was said, while the other person steadfastly denies it, leading to a messy game of "he said, she said."
Once you get to that point, without any written proof, it becomes very hard to win your case. The judge was not there, and if all that is offered is your word on both sides, choosing who is right and who is lying -- or unintentionally skirting the truth -- is nearly impossible.
While oral contracts may still be used between friends, any real business deals should always be put down in writing, even if no dispute is anticipated. You never know what is going to happen, so it pays to be safe.
Make sure you know exactly what elements a written contract has to contain in Calgary so that any paperwork you draft holds up in court.
Source: FIndLaw, "What Contracts are Required to Be in Writing?," accessed July 31, 2015