NOTE - if using a different brand of brownie mix use the suggested ingredient amounts on the box.
In a large bowl add the brownie mix, oil, water and eggs. Mix with a wooden spoon or spatula until smooth. No need to get all the lumps out.
Spray the slow cooker with non stick spray.
Spread the brownie mix in the slow cooker.
Cook on HIGH for 2 hours or until the brownies are set in the middle; every slow cooker cooks slightly differently.
When the cooking time is done. You can serve the brownies hot or you can let them cool and cut into squares.
Notes
If you want a bit of a crunch, consider adding crushed walnuts or pecans. You can also add milk chocolate chips, heath bar chunks or dried cherries.
Any box mix can be used, even gluten-free. However, to ensure the correct consistency, you'll want to use the ingredients listed on the box.
Place any remaining brownies in an airtight container and keep on the countertop up to 4 days. You can also refrigerate them. If you do refrigerate them, you can put them in the microwave to reheat slightly.