Leaks can happen inside a refrigerator if a poorly closed condiment bottle falls over or a forgotten tomato in the back of a drawer starts to ooze. Leaks from under a refrigerator are far more serious, especially if you find black, oily stuff coming from beneath the refrigerator.
A black, oily substance leaking from under a refrigerator is caused by either a water leak from the drip pan beneath the appliance or an oil leak from the refrigeration system. The drip pan catches condensate water that drains from the freezer. If the drip pan has mold or greasy buildup from lack of cleaning, it can leak blackened water out from the refrigerator. If a seal in the refrigeration system fails, oxygen can get into the refrigeration oil, dirtying it and turning it black. When the dirty oil leaks out of the system, it can run out under the refrigerator.
If the problem is from the drip pan, then the water under the appliance could damage the room's flooring. If the drip pan is inundated with mold or grease, then the pan, its contents and the substance that leaks from it are health issues for everyone inside the home. Also, the leaking substance is a slip hazard.
If the refrigerator is damaged to the point it leaks oil, then the refrigeration system has been compromised. The unit will run all the time and fail to maintain an even cool temperature. If not addressed, the compressor could start to burn out.
If the black, oily substance leaks from the drip pan, then the solution is to remove the pan from under the refrigerator and wash it with dish soap and water. A drip pan with cracks or holes needs to be replaced.
If the substance coming from under the refrigerator is oil, then unplug the refrigerator and contact a refrigerator repair specialist. Allowing the appliance to run before it is repaired can damage it further.
If water leaks from a cleaned drip pan or replacement drip pan, then the refrigerator has a water leak. The most likely source is the ice maker in the freezer. Contact a repair specialist to fix the leak. I
If the issue is oil leaking from the refrigeration system, consider the appliance's age before making costly repairs. It might be more cost-effective to purchase a new refrigerator than to repair a damaged old refrigerator.