of coarse, there is a more reasonable response. some oil change places check and top of all of your fluids for you. some of those people can get pretty dumb. some idiot my have dumped some oil in there. but it is safer to probably say equipment failure. check your oil, and note how often youi have to fill it compared to the size of the puddle that resides under the car. yet, if it is the head gasket, you have a leak in your cooling system somewhere, causing the system to loose pressure, causing oil to get into the cooling system, instead of the other way around. good luck. by the way, an oil cooler is a good explanation too.