Comma separated JOIN syntax

When using JOINS by the simply supplying a comma separated list of tables in the FROM clause, is the ON argument normally associated with a join intended to be addressed in the WHERE clause, or should ON still be used? // Comma separated join SELECT u.*, a.city FROM users u, addresses a WHERE u.id=a.user_id; // Actual JOIN clause SELECT u.*, a.city FROM users u INNER JOIN addresses a ON u.id=a.user_id; // Query style in question SELECT u.*, a.city FROM users u, addresses a ON u.id=a.user_id; If not ON, is there at least another viable argument? The reason I'm interested is for a query involving 5 or 6 tables and WHERE arguments which do not deal with the relationships. I would like to assure the efficiency of this query. Thanks in advance, Matt