[DerekM]

OmniOutliner will use the width of the document window for the width of the print out. To get consistent results, make sure print scaling is turned off (File -> Page Setup -> Settings: OmniOutliner -> General tab -> Uncheck 'scale to fit page width'). When that's off, you'll see page break indicators when you resize the width of the window. Setting the width to the first page break will make your document print on a single page and appear like it is shown on screen.

If you have any questions about this, please let me know.