CREATE TABLE table_59729 ("Name  ( year commissioned ) " CLOB, "Owner/operator" CLOB, "Length" CLOB, "Maximum diameter" CLOB, "From/to" CLOB, "Licence number" CLOB)

What is the maximum diameter of the Mid West Gas Pipeline (1999)?
SELECT "Maximum diameter" FROM table_59729 WHERE "Name (year commissioned)" = 'mid west gas pipeline (1999)'
SELECT "Maximum diameter" FROM "table_59729" WHERE "Name (year commissioned)" = 'mid west gas pipeline (1999)'