. these loans are collateralized primarily by 1-4 family residential properties . as part of our asset and liability management activities , we also periodically purchase residential mortgage loans that are collateralized by 1-4 family residential properties . at december 31 , 2007 , $ 3.0 billion of the $ 9.6 billion of residential mortgage loans were interest- only loans . we realized net gains from sales of commercial mortgages of $ 39 million in 2007 , $ 55 million in 2006 and $ 61 million in 2005