I just checked my oil and it smells like gasoline. What does this mean?

In response to your answer what caused the small amount of fuel to get mixed into the oil where I will need a new oil filter?

Hi Roy thanks for answering my questions. And yes to your question, the car is running kind of hard. I recently had an oil change and new sparkplugs added. I thought this would help the car to run more smoothly but it still runs kind of hard. Mechanically speaking, what caused the gasoline to mix is it a seal problem or something similar?