Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_15 ( grid INTEGER, time_retired VARCHAR, laps VARCHAR )

### Question ###
what is the grid when the time/retired is oil pressure and the laps are more than 50?

### Accurate SQL ###

SELECT AVG(grid) FROM table_name_15 WHERE time_retired = "oil pressure" AND laps > 50