Genworth Australia has run out of puff in the price leadership stakes, and says it will not increase premium rates on lenders mortgage insurance over the rest of this year.The prospectus for the long-planned sale of up to 40 per cent of the company in an ASX listing confirms that "in recent years, Genworth Australia increased premium rates [four times in six years] while tightening credit standards."However, it said that under "supply and service contracts with its three largest lender customers (all major banks)" it was constrained from doing so. It said it was also "limited by competitive market forces and other reasons." Its ratio of gross written premium to net insurance written was 1.73 per cent in 2013, more than double the level in 2005, and a rise of 40 basis points over four years.Genworth is the leading supplier in what is, for practical purposes, a duopoly. QBE is the other.The company insured around A$300 billion in loans for lenders at December 2013. This duopoly is so successful it has seen off three US challengers over recent years: MGIC (which financed the LMI predecessor of QBE in the 1960s), Radian and AIG. A few banks operate captive mortgage insurance arms, but the giants often help run these. One that acted with too little outside help, by Wide Bay, is being wound up. Lenders mortgage insurance business is also a seller's market. APRA and the boards of banks mostly insist on mortgage insurance to cover loans when the borrower has little equity.So its surprising its underlying return on equity was 10.4 per cent in the year to December 2013. Genworth expects this to decline to 10.2 per cent this year.The net profit last year was A$179 million. This should recover to $231 million this year. The ROE will still be lower, not because Genworth will be using more capital but because, like banks, it measures underlying profit in a weird way.Demand for its core product is picking up since, "towards the end of 2012, lenders started to remove the restrictions they had put in place for loans with an LVR 90 per cent and above."However, demand for pool insurance on mortgage-backed securities has waned, with major banks opting not to purchase this insurance to support bond issues.Genworth said its top three lender customers accounted for 66 per cent of its gross written premium in 2013, a share that is increasing. Its largest customer (presumably Commonwealth Bank) accounted for 43 per cent of business.