The SQL for Oracle should be

SELECT Assets.asnum, Assets.sub, Assets.aexistnum, Assets.asdes,;
       Assets.asser, Assets.aloc, Assets.adep, Assets.price, Assets.invoice,;
       Assets.acost, Assets.Trans_sold, Locate.locphone, Locate.person, Locate.exist, Udep.desc1;
       FROM  locate, assets, udep ;
         WHERE Locate.locnum = Assets.aloc;
           AND Udep.dep = Assets.adep ;
           AND Assets.adep = madep;
           AND Assets.astyp = mastyp;
           AND Assets.aloc = mloc;
           AND (Assets.trans_sold = " " OR  Assets.trans_sold = "I") ;
       ORDER BY Assets.adep, Assets.aloc, Assets.asnum

The first 2 expressions in the WHERE clause join the 3 tables. You also need to remove the periods from around the OR.