Following in the footsteps of rival State Street (STT:NYSE - commentary - research), the leading exchange-traded fund house is rolling out a gold- linked ETF. The iShares Comex Gold Trust (IAU:Amex - commentary - research) ETF began trading on the American Stock Exchange Friday. Each share in the iShares Comex Gold fund will correspond to one-tenth of a troy ounce of gold. The ETF's trustee, the Bank of New York, will value the trust's gold on the basis of that day's announced Comex settlement price for the spot month gold futures contract. The shares of the trust willl reflect the price of the gold owned by the trust, minus expenses and liabilities. "Obviously the first ETF to market has a much greater advantage," says Michael Porter, ETF analyst at Lipper. "But I expect this to be a successful product for BGI due to their expertise and powerful iShares brand." BGI is the leader in ETFs, with more than $111 billion in assets. State Street Global Advisors is second with $73 billion. State Street's streetTracks Gold (GLD:NYSE - commentary - research) ETF started trading on the New York Stock Exchange in November. The GLD is sponsored by a unit of the World Gold Council and enables investors to participate in the gold bullion market, with each share representing one- tenth of an ounce of gold. The GLD has quickly raised more than $2 billion in assets. Both ETFs have expense ratios of 0.4%. Shares of the IAU last traded at $42.67.