http://www.gomr.mms.gov/homepg/pubin...ed/platloc.zip
This is a zipped file, giving more info than you want to know about platforms in the Gulf of Mexico, including lat & lon. It's from the US Minerals Management Service. The US government makes all sorts of information available for free, including the data on all airports, navaids, intersections, etc for the entire country if you want that.