Add oyster crackers to a 5 quart or larger slow cooker.
In a small bowl whisk together with a fork the oil, garlic and ranch dressing mix until there are no lumps of the ranch dressing mix.
Stirring while you pour, slowly add the liquid over the oyster crackers in the slow cooker making sure all of the crackers are evenly coated in the ranch dressing mixture.
Cover and cook on LOW for 30 minutes, stirring at least once halfway through the cooking time.
Turn slow cooker off and using oven mitts, carefully remove the stoneware crock from the slow cooker and pour oyster crackers out on a rimmed baking sheet that has been lined with parchment or wax paper.
Allow crackers to fully cool and then package them up in seal-able food storage bags or containers for up to 2 weeks.