My car won't start. There is gasoline mixing with the oil. What is causing this to happen?

I had several mechanics look at the car. They all have different opinions on why I am having this problem. Fuel is getting to the engine. When the dipstick for the oil was pulled, there was way over the full mark. The mechanic who discovered that said there was gasoline in the oil. I am a female who knows nothing about engines or cars. I need help.