There is nothing announced for Gate 2018 cut off as it varies year and category wise as well and IOCL does not declare such information as the candidate has to check by login into his account whether he is selected for further rounds or not and for NTPC it was 62.84 and AIR was 206 in previous year.

For reference, you can go through the below article -

https://engineering.careers360.com/articles/what-are-gate-scores-for-psu-recruitment

Good Luck!!!