For an obc category candidate ,the curoff marks in AIIMS 2018 is ecxpected to 115+ /200, however the overall rank matters in AIIMS ,so the rank differs with the morning and evening shifts, so basically answering your question-you have a 70-75% chance of getting a seat in AIIMS 

I hope it helped

BEST OF LUCK FOR RESULTS

dear student,

as per last year cutoff ranking ....you can check here as  per your rank:

Name of AIIMS Institution                                                    rank for obc candidate                       

All India Institute of Medical Sciences, New Delhi                        256

All India Institute of Medical Sciences, Bhopal                        1,170

All India Institute of Medical Sciences, Bhubaneswar                1,034

All India Institute of Medical Sciences, Jodhpur                1,946

All India Institute of Medical Sciences, Patna                2,130

All India Institute of Medical Sciences, Raipur                1,991

All India Institute of Medical Sciences, Rishikesh                2,095

hope it helps.....