Best import format to import posts with excerpts?

I am creating a data feed from an affiliate site which does not provide one of their own for affiliates. Then hopefully trying to import my own created database of items into WordPress. Each post is arranged in a template so it can be easily imported. Now this all works fine and dandy other than the fact that I cannot seem to import the excerpts any ways I have tried. What format works best for importing posts with custom excerpts? The excerpts are an important part of how I have designed my site.