Wesfarmers, owner of Australia's Coles supermarket chain, is offering its first unsecured domestic bond in more than two years. The conglomerate with businesses including retailers, coal mining and insurance, is marketing $300 million of 5 1/2-year fixed-rate bonds at a yield of about 0.95 percentage point more than the swap rate, according to an e- mailed statement from joint sale manager Commonwealth Bank of Australia.