2003 kia serrento* QUESTION

Well me and my husband purchased a used 2003 kia serrento with 59,000 miles on it we have had it for about 3 weeks so far and last week the oil light came on and we checked it and it was dry of oil no oil what so ever so we put more oil it in we filled it up and then a week later dry of oil again. we are taking it back to the car dealer this week but if anyone could tell me what the problem is i know the motor but i need specific detail as to what the problem is.

thanks!